Syria’s war: Everything you need to know about how we got here

By Nick Thompson, CNN
Updated 1:12 PM EST, Thu February 25, 2016
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This image released early Sunday, April 8, 2018 by the Syrian Civil Defense White Helmets, shows a child receiving oxygen through respirators following an alleged poison gas attack in the rebel-held town of Douma, near Damascus, Syria. Syrian rescuers and medics said the attack on Douma killed at least 40 people. The Syrian government denied the allegations, which could not be independently verified. The alleged attack in Douma occurred Saturday night amid a resumed offensive by Syrian government forces after the collapse of a truce. (Syrian Civil Defense White Helmets via AP)
This image released early Sunday, April 8, 2018 by the Syrian Civil Defense White Helmets, shows a child receiving oxygen through respirators following an alleged poison gas attack in the rebel-held town of Douma, near Damascus, Syria. Syrian rescuers and medics said the attack on Douma killed at least 40 people. The Syrian government denied the allegations, which could not be independently verified. The alleged attack in Douma occurred Saturday night amid a resumed offensive by Syrian government forces after the collapse of a truce. (Syrian Civil Defense White Helmets via AP)
PHOTO: Syrian Civil Defense White Helmets/AP
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(CNN) —  

It began with the arrests of a handful of children in 2011. Since then, it’s exploded into the biggest humanitarian crisis since the Second World War.

Syria’s civil war has left more than 300,000 people dead and forced 11.2 million – nearly half the population – out of their homes. How did it come to this? Explore the events that have shaped the crisis since 2011.

It all starts with graffiti

Displaced Syrian residents wait to receive food aid distributed by the UN Relief and Works Agency at the besieged al-Yarmouk camp, south of Damascus, Syria, on January 31, 2014. According to the UN Envoy for Syria, an estimated 400,000 Syrians have been killed since an uprising in March 2011 spiraled into civil war. See how the conflict has unfolded.
Photos: Syria's civil war, in pictures
Displaced Syrian residents wait to receive food aid distributed by the UN Relief and Works Agency at the besieged al-Yarmouk camp, south of Damascus, Syria, on January 31, 2014. According to the UN Envoy for Syria, an estimated 400,000 Syrians have been killed since an uprising in March 2011 spiraled into civil war. See how the conflict has unfolded.
PHOTO: UNRWA/Reuters/Landov
Photos: Syria's civil war, in pictures
An injured man lying in the back of a vehicle is rushed to a hospital in Daraa, Syria, on March 23, 2011. Violence flared in Daraa after a group of teens and children were arrested for writing political graffiti. Dozens of people were killed when security forces cracked down on demonstrations.
Photos: Syria's civil war, in pictures
An injured man lying in the back of a vehicle is rushed to a hospital in Daraa, Syria, on March 23, 2011. Violence flared in Daraa after a group of teens and children were arrested for writing political graffiti. Dozens of people were killed when security forces cracked down on demonstrations.
PHOTO: ANWAR AMRO/AFP/Getty Images
Anti-government protesters demonstrate in Daraa on March 23, 2011. In response to continuing protests, the Syrian government announced several plans to appease citizens.
Photos: Syria's civil war, in pictures
Anti-government protesters demonstrate in Daraa on March 23, 2011. In response to continuing protests, the Syrian government announced several plans to appease citizens.
PHOTO: Hussein Malla/AP
Syrian children walk over bricks stored for road repairs during a spontaneous protest June 15, 2011, at a refugee camp near the Syrian border in Yayladagi, Turkey.
Photos: Syria's civil war, in pictures
Syrian children walk over bricks stored for road repairs during a spontaneous protest June 15, 2011, at a refugee camp near the Syrian border in Yayladagi, Turkey.
PHOTO: Vadim Ghirda/AP
Jamal al-Wadi speaks in Istanbul on September 15, 2011, after an alignment of Syrian opposition leaders announced the creation of a Syrian National Council -- their bid to present a united front against Bashar al-Assad
Photos: Syria's civil war, in pictures
Jamal al-Wadi speaks in Istanbul on September 15, 2011, after an alignment of Syrian opposition leaders announced the creation of a Syrian National Council -- their bid to present a united front against Bashar al-Assad's regime and establish a democratic system.
PHOTO: Burhan Ozbilici/AP
Delegates from Arab League member states and Turkey discuss a response to the government
Photos: Syria's civil war, in pictures
Delegates from Arab League member states and Turkey discuss a response to the government's crackdown in Syria on November 16, 2011.
PHOTO: ABDELHAK SENNA/AFP/Getty Images
Supporters of al-Assad celebrate during a referendum vote in Damascus on February 26, 2012. Opposition activists reported at least 55 deaths across the country as Syrians headed to the polls. Analysts and protesters widely described the constitutional referendum as a farce. "Essentially, what (al-Assad
Photos: Syria's civil war, in pictures
Supporters of al-Assad celebrate during a referendum vote in Damascus on February 26, 2012. Opposition activists reported at least 55 deaths across the country as Syrians headed to the polls. Analysts and protesters widely described the constitutional referendum as a farce. "Essentially, what (al-Assad's) done here is put a piece of paper that he controls to a vote that he controls so that he can try and maintain control," a US State Department spokeswoman said.
PHOTO: KHALED AL-HARIRI/Reuters/LANDOV
Syrian refugees walk across a field in Syria before crossing into Turkey on March 14, 2012.
Photos: Syria's civil war, in pictures
Syrian refugees walk across a field in Syria before crossing into Turkey on March 14, 2012.
PHOTO: BULENT KILIC/AFP/Getty Images
Rebel fighters with the Free Syrian Army capture a police officer in Aleppo, Syria, who they believed to be pro-regime militiaman on July 31, 2012. Dozens of officers were reportedly killed as rebels seized police stations in the city.
Photos: Syria's civil war, in pictures
Rebel fighters with the Free Syrian Army capture a police officer in Aleppo, Syria, who they believed to be pro-regime militiaman on July 31, 2012. Dozens of officers were reportedly killed as rebels seized police stations in the city.
PHOTO: EMIN OZMEN/AFP/Getty Images
A Free Syrian Army fighter runs for cover as a Syrian Army tank shell hits a building across the street during clashes in the Salaheddine neighborhood of central Aleppo on August 17, 2012.
Photos: Syria's civil war, in pictures
A Free Syrian Army fighter runs for cover as a Syrian Army tank shell hits a building across the street during clashes in the Salaheddine neighborhood of central Aleppo on August 17, 2012.
PHOTO: GORAN TOMASEVIC/Reuters/Landov
Family members mourn the deaths of their relatives in front of a field hospital in Aleppo on August 21, 2012.
Photos: Syria's civil war, in pictures
Family members mourn the deaths of their relatives in front of a field hospital in Aleppo on August 21, 2012.
PHOTO: Edouard Elias/Getty Images
A Syrian man carrying grocery bags dodges sniper fire in Aleppo as he runs through an alley near a checkpoint manned by the Free Syrian Army on September 14, 2012.
Photos: Syria's civil war, in pictures
A Syrian man carrying grocery bags dodges sniper fire in Aleppo as he runs through an alley near a checkpoint manned by the Free Syrian Army on September 14, 2012.
PHOTO: MARCO LONGARI/AFP/Getty Images
Free Syrian Army fighters are reflected in a mirror they use to see a Syrian Army post only 50 meters away in Aleppo on September 16, 2012.
Photos: Syria's civil war, in pictures
Free Syrian Army fighters are reflected in a mirror they use to see a Syrian Army post only 50 meters away in Aleppo on September 16, 2012.
PHOTO: MARCO LONGARI/AFP/Getty Images
Smoke rises over the streets after a mortar bomb from Syria landed in the Turkish border village of Akcakale on October 3, 2012. Five people were killed. In response, Turkey fired on Syrian targets and its parliament authorized a resolution giving the government permission to deploy soldiers to foreign countries.
Photos: Syria's civil war, in pictures
Smoke rises over the streets after a mortar bomb from Syria landed in the Turkish border village of Akcakale on October 3, 2012. Five people were killed. In response, Turkey fired on Syrian targets and its parliament authorized a resolution giving the government permission to deploy soldiers to foreign countries.
PHOTO: ANADOLU AGENCY/REUTERS//LANDOV
A Syrian rebel walks inside a burnt section of the Umayyad Mosque in Aleppo hours before the Syrian army retook control of the complex on October 14, 2012.
Photos: Syria's civil war, in pictures
A Syrian rebel walks inside a burnt section of the Umayyad Mosque in Aleppo hours before the Syrian army retook control of the complex on October 14, 2012.
PHOTO: TAUSEEF MUSTAFA/AFP/Getty Images
An Israeli tank crew sits on the Golan Heights overlooking the Syrian village of Breqa on November 6, 2012. Israel fired warning shots toward Syria after a mortar shell hit an Israeli military post. It was the first time Israel fired on Syria across the Golan Heights since the 1973 Yom Kippur War.
Photos: Syria's civil war, in pictures
An Israeli tank crew sits on the Golan Heights overlooking the Syrian village of Breqa on November 6, 2012. Israel fired warning shots toward Syria after a mortar shell hit an Israeli military post. It was the first time Israel fired on Syria across the Golan Heights since the 1973 Yom Kippur War.
PHOTO: MENAHEM KAHANA/AFP/Getty Images
Smoke rises in the Hanano and Bustan al-Basha districts in Aleppo as fighting continues through the night on December 1, 2012.
Photos: Syria's civil war, in pictures
Smoke rises in the Hanano and Bustan al-Basha districts in Aleppo as fighting continues through the night on December 1, 2012.
PHOTO: Javier Manzano/AFP/Getty Images
The bodies of three children are laid out for identification by family members at a makeshift hospital in Aleppo on December 2, 2012. The children were allegedly killed in a mortar shell attack that landed close to a bakery in the city.
Photos: Syria's civil war, in pictures
The bodies of three children are laid out for identification by family members at a makeshift hospital in Aleppo on December 2, 2012. The children were allegedly killed in a mortar shell attack that landed close to a bakery in the city.
PHOTO: Javier Manzano/AFP/Getty Images
A father reacts after the deaths of two of his children in Aleppo on January 3, 2013.
Photos: Syria's civil war, in pictures
A father reacts after the deaths of two of his children in Aleppo on January 3, 2013.
PHOTO: MUZAFFAR SALMAN/Reuters/Landov
Syrians look for survivors amid the rubble of a building targeted by a missile in the al-Mashhad neighborhood of Aleppo on January 7, 2013.
Photos: Syria's civil war, in pictures
Syrians look for survivors amid the rubble of a building targeted by a missile in the al-Mashhad neighborhood of Aleppo on January 7, 2013.
PHOTO: ACHILLEAS ZAVALLIS/AFP/Getty Images
Rebels launch a missile near the Abu Baker brigade in Al-Bab, Syria, on January 16, 2013.
Photos: Syria's civil war, in pictures
Rebels launch a missile near the Abu Baker brigade in Al-Bab, Syria, on January 16, 2013.
PHOTO: EDOUARD ELIAS/AFP/Getty Images
An aerial view shows the Zaatari refugee camp near the Jordanian city of Mafraq on July 18, 2013.
Photos: Syria's civil war, in pictures
An aerial view shows the Zaatari refugee camp near the Jordanian city of Mafraq on July 18, 2013.
PHOTO: MANDEL NGAN/AFP/Getty Images
The UN Security Council passes a resolution September 27, 2013, requiring Syria to eliminate its arsenal of chemical weapons. Al-Assad said he would abide by the resolution.
Photos: Syria's civil war, in pictures
The UN Security Council passes a resolution September 27, 2013, requiring Syria to eliminate its arsenal of chemical weapons. Al-Assad said he would abide by the resolution.
PHOTO: STAN HONDA/AFP/Getty Images
Residents run from a fire at a gasoline and oil shop in Aleppo
Photos: Syria's civil war, in pictures
Residents run from a fire at a gasoline and oil shop in Aleppo's Bustan Al-Qasr neighborhood on October 20, 2013. Witnesses said the fire was caused by a bullet from a pro-government sniper.
PHOTO: Haleem Al-Halabi/Reuters/Landov
Syrian children wait as doctors perform medical checkups at a refugee center in Sofia, Bulgaria, on October 26, 2013.
Photos: Syria's civil war, in pictures
Syrian children wait as doctors perform medical checkups at a refugee center in Sofia, Bulgaria, on October 26, 2013.
PHOTO: STOYAN NENOV/Reuters/LANDOV
An injured man is helped following an airstrike in Aleppo
Photos: Syria's civil war, in pictures
An injured man is helped following an airstrike in Aleppo's Maadi neighborhood on December 17, 2013.
PHOTO: MOHAMMED AL-KHATIEB/AFP/Getty Images
A man holds a baby who was rescued from rubble after an airstrike in Aleppo on February 14, 2014.
Photos: Syria's civil war, in pictures
A man holds a baby who was rescued from rubble after an airstrike in Aleppo on February 14, 2014.
PHOTO: Hosam Katan/Reuters/Landov
A US ship staff member wears personal protective equipment at a naval airbase in Rota, Spain, on April 10, 2014. A former container vessel was fitted out with at least $10 million of gear to let it take on about 560 metric tons of Syria
Photos: Syria's civil war, in pictures
A US ship staff member wears personal protective equipment at a naval airbase in Rota, Spain, on April 10, 2014. A former container vessel was fitted out with at least $10 million of gear to let it take on about 560 metric tons of Syria's most dangerous chemical agents and sail them out to sea, officials said.
PHOTO: Marcelo del Pozo/Reuters/Landov
A Free Syrian Army fighter fires a rocket-propelled grenade during heavy clashes in Aleppo on April 27, 2014.
Photos: Syria's civil war, in pictures
A Free Syrian Army fighter fires a rocket-propelled grenade during heavy clashes in Aleppo on April 27, 2014.
PHOTO: Jalal Al-Mamo/Reuters/Landov
A giant poster of al-Assad is seen in Damascus on May 31, 2014, ahead of the country
Photos: Syria's civil war, in pictures
A giant poster of al-Assad is seen in Damascus on May 31, 2014, ahead of the country's presidential elections. He received 88.7% of the vote in the country's first election after the civil war broke out.
PHOTO: Pan Chaoyue/Xinhua/Landov
Rebel fighters execute two men on July 25, 2014, in Binnish, Syria. The men were reportedly charged by an Islamic religious court with detonating several car bombs.
Photos: Syria's civil war, in pictures
Rebel fighters execute two men on July 25, 2014, in Binnish, Syria. The men were reportedly charged by an Islamic religious court with detonating several car bombs.
PHOTO: AMR RADWAN AL-HOMSI/AFP/Getty Images
Photographs of victims of the Assad regime are displayed as a Syrian army defector known as "Caesar," center, appears in disguise to speak before the House Foreign Affairs Committee in Washington. The July 31, 2014, briefing was called "Assad
Photos: Syria's civil war, in pictures
Photographs of victims of the Assad regime are displayed as a Syrian army defector known as "Caesar," center, appears in disguise to speak before the House Foreign Affairs Committee in Washington. The July 31, 2014, briefing was called "Assad's Killing Machine Exposed: Implications for U.S. Policy." Caesar, apparently a witness to the regime's brutality, smuggled more than 50,000 photographs depicting the torture and execution of more than 10,000 dissidents. CNN cannot independently confirm the authenticity of the photos, documents and testimony referenced in the report.
PHOTO: Andrew Harnik/The Washington Times/Landov
Volunteers remove a dead body from under debris after shelling in Aleppo on August 29, 2014. According to the Syrian Civil Defense, barrel bombs are now the greatest killer of civilians in many parts of Syria. The White Helmets are a humanitarian organization that tries to save lives and offer relief.
Photos: Syria's civil war, in pictures
Volunteers remove a dead body from under debris after shelling in Aleppo on August 29, 2014. According to the Syrian Civil Defense, barrel bombs are now the greatest killer of civilians in many parts of Syria. The White Helmets are a humanitarian organization that tries to save lives and offer relief.
PHOTO: Abdalrhman Ismail/Reuters/Landov
Medics tend to a man
Photos: Syria's civil war, in pictures
Medics tend to a man's injuries at a field hospital in Douma after airstrikes on September 20, 2014.
PHOTO: Badra Mamet/Reuters/Landov
A long-exposure photograph shows a rocket being launched in Aleppo on October 5, 2014.
Photos: Syria's civil war, in pictures
A long-exposure photograph shows a rocket being launched in Aleppo on October 5, 2014.
PHOTO: Rami Zayat/Reuters/Landov
Rebel fighters dig caves in the mountains for bomb shelters in the northern countryside of Hama on March 9, 2015.
Photos: Syria's civil war, in pictures
Rebel fighters dig caves in the mountains for bomb shelters in the northern countryside of Hama on March 9, 2015.
PHOTO: KHALIL ASHAWI/Reuters/LANDOV
Nusra Front fighters inspect a helicopter belonging to pro-government forces after it crashed in the rebel-held Idlib countryside on March 22, 2015.
Photos: Syria's civil war, in pictures
Nusra Front fighters inspect a helicopter belonging to pro-government forces after it crashed in the rebel-held Idlib countryside on March 22, 2015.
PHOTO: Abed Kontar/Reuters/Landov
A Syrian child fleeing the war gets lifted over fences to enter Turkish territory illegally near a border crossing at Akcakale, Turkey, on June 14, 2015.
Photos: Syria's civil war, in pictures
A Syrian child fleeing the war gets lifted over fences to enter Turkish territory illegally near a border crossing at Akcakale, Turkey, on June 14, 2015.
PHOTO: Bulent Kilic/AFP/Getty Images
A refugee carries mattresses as he re-enters Syria from Turkey on June 22, 2015, after Kurdish People
Photos: Syria's civil war, in pictures
A refugee carries mattresses as he re-enters Syria from Turkey on June 22, 2015, after Kurdish People's Protection Units regained control of the area around Tal Abyad, Syria, from ISIS.
PHOTO: Uygar Onder Simsek/AFP/Getty Images
A sandstorm blows over damaged buildings in the rebel-held area of Douma, east of Damascus, on September 7, 2015.
Photos: Syria's civil war, in pictures
A sandstorm blows over damaged buildings in the rebel-held area of Douma, east of Damascus, on September 7, 2015.
PHOTO: SAMEER AL-DOUMY/AFP/Getty Images
Members of a Syrian opposition group attack the headquarters of al-Assad regime forces in the Aleppo villages of Nubul and al-Zahraa on February 12, 2016.
Photos: Syria's civil war, in pictures
Members of a Syrian opposition group attack the headquarters of al-Assad regime forces in the Aleppo villages of Nubul and al-Zahraa on February 12, 2016.
PHOTO: Mustafa Sultan /Anadolu Agency/Getty Images
This still image, taken from a video posted by the Aleppo Media Center, shows a young boy in an ambulance after an airstrike in Aleppo, Syria, on August 17, 2016. It took nearly an hour to dig the boy, identified as Omran Daqneesh, out from the rubble, an activist told CNN. The airstrike destroyed his home, where he lived with his parents and two siblings. Director of the Aleppo Media Center Yousef Saddiq said Omran
Photos: Syria's civil war, in pictures
This still image, taken from a video posted by the Aleppo Media Center, shows a young boy in an ambulance after an airstrike in Aleppo, Syria, on August 17, 2016. It took nearly an hour to dig the boy, identified as Omran Daqneesh, out from the rubble, an activist told CNN. The airstrike destroyed his home, where he lived with his parents and two siblings. Director of the Aleppo Media Center Yousef Saddiq said Omran's 10-year-old brother, Ali, died from his injuries.
PHOTO: Mahmud Rslan/Anadolu Agency/Getty Images
Smoke rises after an airstrike in Aleppo on October 4, 2016.
Photos: Syria's civil war, in pictures
Smoke rises after an airstrike in Aleppo on October 4, 2016.
PHOTO: Mahmud Faysal/Anadolu Agency/Getty Images
Arabic writing that reads "some day we will return" is seen on a bus window as civilians evacuate Aleppo on December 15, 2016. The evacuations began under a new ceasefire between rebels and pro-government forces.
Photos: Syria's civil war, in pictures
Arabic writing that reads "some day we will return" is seen on a bus window as civilians evacuate Aleppo on December 15, 2016. The evacuations began under a new ceasefire between rebels and pro-government forces.
PHOTO: KARAM AL-MASRI/AFP/Getty Images
This photo, provided by the activist Idlib Media Center, shows dead children after a suspected chemical attack in the rebel-held city of Khan Sheikhoun on April 4, 2017. Dozens of people were killed, according to multiple activist groups. The United States responded a few days later by launching between 50-60 Tomahawk missiles at a Syrian government airbase. US officials said the base was home to warplanes that carried out the chemical attack. Syria has repeatedly denied it had anything to do with the attack.
Photos: Syria's civil war, in pictures
This photo, provided by the activist Idlib Media Center, shows dead children after a suspected chemical attack in the rebel-held city of Khan Sheikhoun on April 4, 2017. Dozens of people were killed, according to multiple activist groups. The United States responded a few days later by launching between 50-60 Tomahawk missiles at a Syrian government airbase. US officials said the base was home to warplanes that carried out the chemical attack. Syria has repeatedly denied it had anything to do with the attack.
PHOTO: Idlib Media Center
Members of the UN Security Council raise their hands on April 12, 2017, as they vote in favor of a draft resolution that condemned the reported use of chemical weapons in Syria.
Photos: Syria's civil war, in pictures
Members of the UN Security Council raise their hands on April 12, 2017, as they vote in favor of a draft resolution that condemned the reported use of chemical weapons in Syria.
PHOTO: KENA BETANCUR/AFP/Getty Images
Residents of the war-torn city of Douma break their Ramadan fast on June 18, 2017.
Photos: Syria's civil war, in pictures
Residents of the war-torn city of Douma break their Ramadan fast on June 18, 2017.
PHOTO: HAMZA AL-AJWEH/AFP/Getty Images
A member of the Syrian pro-regime forces fires a machine gun as a comrade holds his feeding ammunition belt on November 11, 2017. It was during an advance toward rebel-held positions west of Aleppo.
Photos: Syria's civil war, in pictures
A member of the Syrian pro-regime forces fires a machine gun as a comrade holds his feeding ammunition belt on November 11, 2017. It was during an advance toward rebel-held positions west of Aleppo.
PHOTO: GEORGE OURFALIAN/AFP/Getty Images
A child receives medical treatment after a village was attacked in the rebel-held Eastern Ghouta region on February 25, 2018. Several people were treated for exposure to chlorine gas, opposition groups said, as airstrikes and artillery fire from the regime continued. CNN was unable to independently verify claims that chlorine was used as a weapon.
Photos: Syria's civil war, in pictures
A child receives medical treatment after a village was attacked in the rebel-held Eastern Ghouta region on February 25, 2018. Several people were treated for exposure to chlorine gas, opposition groups said, as airstrikes and artillery fire from the regime continued. CNN was unable to independently verify claims that chlorine was used as a weapon.
PHOTO: MOHAMMED BADRA/EPA
Bodies lie on the ground in the rebel-held city of Douma, Syria, on April 8, 2018. According to activist groups, helicopters dropped barrel bombs filled with toxic gas on Douma, which has been the focus of a renewed government offensive that launched in mid-February. The Syrian government and its key ally, Russia, vehemently denied involvement and accused rebel groups of fabricating the attack to hinder the army
Photos: Syria's civil war, in pictures
Bodies lie on the ground in the rebel-held city of Douma, Syria, on April 8, 2018. According to activist groups, helicopters dropped barrel bombs filled with toxic gas on Douma, which has been the focus of a renewed government offensive that launched in mid-February. The Syrian government and its key ally, Russia, vehemently denied involvement and accused rebel groups of fabricating the attack to hinder the army's advances and provoke international military intervention.
PHOTO: EMAD ALDIN/EPA
Damascus skies erupt with anti-aircraft fire as the US and its allies launch an attack on Syria
Photos: Syria's civil war, in pictures
Damascus skies erupt with anti-aircraft fire as the US and its allies launch an attack on Syria's capital early on April 14, 2018. US President Donald Trump announced airstrikes in retaliation for Syria's alleged use of chemical weapons. Trump says the strikes are part of a sustained military response, in coordination with France and the United Kingdom.
PHOTO: Hassan Ammar/AP

February 2011: As Arab Spring demonstrations overthrow governments across the Middle East, a group of children in Daraa, southern Syria, are arrested and allegedly tortured for scrawling graffiti on a school reading “the people want to topple the regime.”

Outrage over the arrests turns into protests and a brutal crackdown

Protesters clash with Syrian security forces on the streets of Daraa in March 2011.
Protesters clash with Syrian security forces on the streets of Daraa in March 2011.
PHOTO: ANWAR AMRO/AFP/Getty Images

March 2011: Syrians protest in cities across the country, demanding the government enact reforms and release political protesters. Government forces fire on the demonstrations, killing dozens.

As the bloodshed gets worse, the opposition gets organized

July 2011: As the government crackdown intensifies, a group of Syrian military officers defect and form the Free Syrian Army. In a video posted on YouTube, they say thousands of soldiers have left their posts instead of firing on protesters, and they promise to wage guerrilla war against regime forces. Three months later, a handful of political opposition groups establish the Syrian National Council, aimed at toppling President Bashar al-Assad.

The West calls for Assad to quit, but Russia and China have other ideas

August-October 2011: Top U.S. and European leaders call for Assad to step down, saying Syria’s future “must be determined by its own people.” But in October, Russia and China veto a U.N. Security Council resolution supported by the United States that would call for an immediate halt to violence and immediate sanctions.

Meanwhile, the influence of Islamist groups grows in rebel ranks

December 2011 to February 2012: Suicide bombers kill 44 people in Damascus in blasts that bear the “blueprints of al Qaeda,” the government says. In February the leader of al Qaeda, Ayman al-Zawahiri, praises Syrians for waging “jihad.” The message comes as thousands of rebels join more extreme groups now operating in the country, including Jabhat al-Nusra, a group with close links to al Qaeda’s affiliate in Iraq.

The U.N. brokers a ceasefire that falls apart almost immediately

April 2012: Former United Nations chief Kofi Annan brokers a ceasefire plan calling for a halt to violence and the implementation of a political process to end the crisis, but the plan never gets off the ground.

As refugees flee, the U.N. accuses Syria of crimes against humanity

June to July 2012: A top U.N. human rights official accuses Syria of engaging in crimes against humanity. A month later, the Zaatari refugee camp opens in Jordan to house the thousands of refugees streaming across the border from Syria.

Barack Obama announces his ‘red line’ in Syria for the first (but not last) time

August 2012: President Obama says President Assad will be crossing a “red line” if he uses chemical weapons against his own people in Syria. Syria has one of the largest and most advanced chemical warfare programs in the Arab world, according to experts.

Two years in, 60,000 are dead, and the U.S. says it will send aid to rebels

February 2013: The U.S. promises to send food and medical supplies – but not weapons – to Syrian rebels. It’s the first such move since the conflict began two years before, in an effort to hem in the radical Islamist groups vying for influence in Syria. More than 60,000 people are now dead and nearly a million have fled the country.

ISIS emerges in Syria

Spring 2013: The Islamic State in Iraq and Syria (ISIS) announces its arrival in northern Syria by seizing the city of Raqqa. The group began in 2004 as al Qaeda in Iraq before rebranding as ISIS two years later. The aim of ISIS – led by Abu Bakr al-Baghdadi – is to impose its strict Islamist ideology on Syrians in the areas it controls.

European nations join the list of countries sending weapons into Syria

May 2013: The EU lifts its arms embargo on Syria, clearing the way for European nations to join Saudi Arabia, Qatar and other countries that have provided weapons or training to rebel groups in Syria. Russia, meanwhile, is shipping arms to the Syrian regime, and fighters from Hezbollah – the Iranian-backed Lebanese militant group – pour into the country to prop up the regime in Syria, a key ally.

Syria crosses Obama’s ‘red line,’ and the U.S. prepares to attack

August 2013: Hundreds of people are killed in a suspected chemical weapons attack in rebel-held areas on the outskirts of Damascus. Obama asks Congress to authorize military action against Syria.

John Kerry goes off script, and the Russians pounce

September 2013: U.S. airstrikes seem inevitable. Asked what, if anything, the Syrian regime can do to stop an attack, U.S. Secretary of State John Kerry says Assad “could turn over every single bit of his chemical weapons to the international community in the next week.” Russia immediately proposes putting Syria’s chemical weapons under international control, a plan that staves off U.S. military action in the country for the time being.

140,000 are dead in Syria as peace talks go nowhere fast

February 2014: A second round of peace talks between the Syrian government, the opposition and an array of world powers ends without a solution. At least 140,000 Syrians are now dead, opposition groups say, and hundreds of thousands have been displaced.

ISIS declares an independent state in Iraq and Syria

June 2014: ISIS announces the establishment of a caliphate (Islamic state) stretching from western Syria to eastern Iraq. The group rebrands itself Islamic State and says Abu Bakr al-Baghdadi is the leader of this new state. The declaration comes after ISIS seizes Mosul, Iraq’s second-biggest city.

ISIS beheads American journalist James Foley

August 2014: ISIS releases a video showing the beheading of American journalist James Foley in Raqqa, Syria. Foley is the first of several Western journalists and aid workers to be murdered by the group over the next few months, including Steven Sotloff, David Haines, Alan Henning and Peter Abdul-Rahman Kassig.

The U.S. launches airstrikes on ISIS in Syria

September 2014: American jets begin bombing ISIS targets in Syria, including the group’s stronghold in Raqqa. The foreign partners participating in the strikes are Arab countries, including Saudi Arabia, Jordan, Bahrain and the United Arab Emirates.

Kurdish forces, backed by U.S. strikes, take back Kobani from ISIS

January 2015: Kurdish fighters retake Kobani, a key Syrian town on the Turkish border, after nearly four months of fighting with ISIS.

ISIS seizes Palmyra and blows up its priceless ruins

May-August 2015: ISIS seizes Palmyra and blows up many of the ancient desert city’s millennia-old temples and shrines. The group executes dozens of people in the city’s ancient amphitheater, and beheads an antiquities expert who refused to reveal the location of other archaeological treasures.

Russia launches airstrikes in Syria

The stakes are enormous. More than 250,000 people have died in Syria in the past five years. Half the country has been uprooted and fled. And unless drastic changes happen soon, the death and destruction will continue unabated.

Turkey downs Russian jet over Syria

November 24, 2015: Turkey shoots down a Russian Su-24 warplane over Syria, saying it had violated Turkish airspace. The incident triggers a war of words and escalating tensions between the two powers, who back opposite sides in the Syrian conflict.

Europe hits 1 million refugees in 2015

December, 2015: The number of migrants who have entered Europe by sea and land in 2015 passes 1 million, the International Organization for Migration says, with about half of them Syrians fleeing the conflict. The surge in migrants poses a crisis for European nations, with governments split on how to respond.

Donors pledge more than $10 billion to Syria

February 4, 2016: More than $10 billion is pledged for Syria by international donors at a conference in London. But the goodwill is overshadowed a brutal Syrian government offensive, backed by Russian air power, on the northern city of Aleppo, which Turkey says has sent a fresh wave of refugees fleeing toward its border.

World powers agree to ‘cessation of hostilities’

February 11, 2016: Diplomats from more than a dozen countries, including the United States and Russia, agree in Munich, Germany, to a “cessation of hostilities” – a temporary halt in fighting that commonly happens at the start of a peace process – and to the delivery of aid. Terrorist groups, including ISIS and al-Nusra, are not included in the deal. The partial truce does not take hold a week later as originally hoped, but there are renewed efforts to implement the deal the following Friday.