(CNN) -- Here's a look at what you need to know about Yemen, which is located on the southwestern tip of the Arabian Peninsula and shares a border with Saudi Arabia and Oman.
About Yemen: (from the CIA World Fact Book) Area: 527,968 sq km (slightly larger than twice the size of Wyoming)
Population: 25,338,458 (July 2013 est.)
Median age: 18.5 years
Ethnic Groups: Predominantly Arab, also Afro-Arab, South Asian, European
GDP: $58.27 billion (2012 est.)
GDP per capita: $2,300 (2012 est.)
Unemployment: 35% (2003 est.)
Other Facts: Yemen is one of the poorest countries in the Arab world, due to declining oil resources.
Yemen's economy depends on foreign aid and money sent home by Yemenis who are employed in other parts of the Arabian Peninsula.
Most Yemenis are farmers, herders or craftsmen.
Yemen is part of the Arab League.
Timeline: May 22, 1990 - The Republic of Yemen is created from unification of North Yemen, the People's Democratic Republic of Yemen (PDRY), and South Yemen, or the Yemen Arab Republic (YAR).
April 1993 - Elections are held after postponement due to political turmoil.
May 1994 - A civil war between northerners and southerners begins due to disagreements between supporters of Yemen's president, Ali Abdullah Saleh, from North Yemen, and its vice president, Ali Salim al-Baid, from South Yemen. An estimated 5,000 people are killed. Troops loyal to Saleh win the war in July.
1998 - Worsening economic conditions contribute to increased militant Islamist activity in the late 1990s. In 1998, 12 tourists were kidnapped, four of whom were murdered. Thereafter, troubles with al Qaeda and similar groups increased.
September 1999 - Saleh wins Yemen's first direct election. He is re-elected in 2006.
2000 - Saudi Arabia and Yemen agree to a delineation of their border.
October 12, 2000 - The U.S.S. Cole, at anchor in Aden, is bombed by al Qaeda, killing 17 U.S. sailors.
October 2002 - Al Qaeda is blamed for an attack on the Limburg, a French-flagged oil tanker off the Yemeni coast.
August 2004 - A Zaydi rebellion erupts in northern Yemen.
February 2006 - Twenty three inmates escape from a prison in Sanaa. Thirteen are convicted al Qaeda members, including Jamal al-Badawi, who plotted the attack on the U.S.S. Cole.
September 17, 2008 - A suicide bombing at the U.S. embassy in Sanaa kills 16, including six terrorists and one American. It is the fourth time since 2003 that the embassy has been attacked.
December 28, 2009 - A Yemeni-based arm of al Qaeda, al Qaeda in the Arabian Peninsula (AQAP), claims responsibility for a failed bombing on a Northwest Airlines flight from Amsterdam to Detroit, Michigan on Christmas.
January 2, 2010 - U.S. President Barack Obama announces a new counter-terrorism partnership with Yemen, involving intelligence sharing, military training and joint attacks.
January 3-5, 2010 - The United States and the United Kingdom temporarily close their embassies in Sanaa due to terror concerns.
February 11, 2011 - Protests begin in Yemen, inspired by the revolution in Egypt that ousted Hosni Mubarak. The demonstrations continue for months, while crackdowns on protesters lead to civilian deaths.
March 20, 2011 - President Ali Abdullah Saleh dismisses his cabinet.
March 23, 2011 - President Saleh offers to step down as president by the end of year. Opposition groups reject his proposal.
April 23, 2011 - President Saleh tentatively accepts a deal, arranged by the Gulf Cooperation Council, to leave office. The agreement states if Saleh resigns the presidency within 30 days, he and members of his regime will be given total immunity.
May 22, 2011 - Saleh again refuses to sign the deal to step down. The Gulf Cooperation Council suspends its efforts to mediate a deal between Saleh and opposition forces.
June 3, 2011 - Opposition forces launch missiles at the presidential palace, injuring President Saleh and killing several others.
June 4, 2011 - Vice President Abdu Rabu Mansour Hadi is left in charge while President Saleh travels to Saudi Arabia to undergo medical treatment.
June 6, 2011 - It is revealed that President Saleh is being treated for burns over 40% of his body and a collapsed lung.
September 2, 2011 - Approximately two million people demonstrate across Yemen, demanding that the military remove President Ali Abdullah Saleh from power.
September 23, 2011 - President Saleh returns to Yemen, after more than three months of medical treatment in Saudi Arabia.
September 30, 2011 - Anwar al-Awlaki, spokesman for al Qaeda in the Arabian Peninsula, is killed by a CIA drone strike eight kilometers from the town of Khashef in the Province of Jawf.
November 23, 2011 - President Saleh signs an agreement in Saudi Arabia transferring his executive powers to Yemen's vice president, Abdu Rabu Mansour Hadi, effectively ending his rule. He is allowed to retain the title of president for 90 days.
January 21, 2012 - Yemen's parliament approves a controversial law that ensures Saleh complete immunity from prosecution. In return, Saleh will step down from power next month.
February 21, 2012 - Yemen holds presidential elections to replace President Ali Abdullah Saleh. There is only one candidate on the ballot, Vice President Abdu Rabu Mansour Hadi, the acting president since November 2011. Hadi receives 99.8% of the 6.6 million votes cast.
February 25, 2012 - Abdu Rabu Mansour Hadi is sworn in as president of Yemen.
February 27, 2012 - The official inauguration of Hadi takes place.
February 29, 2012 - A spokesman for former President Saleh's political party denies rumors that Saleh is planning to leave the country and settle in Ethiopia. Tens of thousands of people have marched near Saleh's home calling for his prosecution and demanding he leave the country over concerns that his presence will undermine the new president.
May 21, 2012 - A suicide bomber attack in Yemen kills over 100 Yemeni troops and wounds more than 200.
May 23, 2012 - Donor countries led by Saudi Arabia and the United Kingdom calling themselves the "Friends of Yemen" pledge more than $4 billion in aid.
January 24, 2013 - The Yemeni government confirms that Saeed al-Shahri, second in command of al Qaeda in the Arabian Peninsula, has died after being wounded on November 28, 2012.
August 7, 2013 - According to a spokesman for the prime minister, Yemen foils an al Qaeda plot to capture oil and gas facilities and seize two key southern ports.
December 15, 2013 - Yemen's parliament calls for an end to drone strikes on its terrority three days after a U.S. missile attack mistakenly struck a wedding convoy, killing more than a dozen people.
February 10, 2014 - President Abdu Rabu Mansour Hadi approves making Yemen a federal state consisting of six regions: two in the south, and four in the more populated north.