(CNN) -- The extremist Sunni militants sweeping across Iraq may have a singular goal, but there's a broad coalition of recruits from outside of the Middle East willing to help them achieve it.
The so-called Islamic State in Iraq and Syria, or ISIS, wants to establish an Islamic state stretching from northern Syria into Iraq. And as the brutal terror group racks up victory after victory on the battlefield, more foreign fighters are considering joining their ranks.
Who are they?
Three young men we spoke to have traveled to Syria to answer the call to jihad. They agreed to speak to us from the northwestern city of Idlib over Skype, provided we masked their identities and didn't use their real names.
Abu Anwar, as he asked to be called, is 25 years old and from Britain.
"I'm from the south of England. I grew up in a middle class family," he told us. "Life was easy back home. I had a life. I had a car. But the thing is: You cannot practice Islam back home. We see all around us evil. We see pedophiles. We see homosexuality. We see crime. We see rape."
We spoke with Abu and his friends as so many of these young men do: online. Their posts, many featuring photos of them posing with guns, attempt to make jihad sound cool. And this is a big draw to many youngsters who want to be part of this war, but have little or no combat experience.
ISIS claims to be fighting for justice, but in reality their campaign is about brutality. The group has committed massacres and acts of terror so extreme -- including a recent boast about executing Iraqi soldiers in cold blood -- that even al Qaeda has disavowed them.
I asked Abu if his family knows what he's doing in Syria.
"They are not happy with me being here. But when I give them Dawa (their interpretation of Islam), they see the reality, they hear the reality from me that they don't hear from the BBC," he replied, after a pause.
There are thousands like Abu from all across Europe in Syria and Iraq, according to some estimates. The Soufan group, a security consulting firm, believes there are around 700 from France, 800 from Russia and almost 300 from Britain. But these figures relate to people analysts have been able to track, and the true numbers may be even higher. And as ISIS's onslaught in Iraq grows, there are fears even more foreigners will be drawn to fight.
Last month, U.S. officials said Moner Mohammad Abu-Salha, a 22-year-old American known as Abu Hurayra Al-Amriki, drove a truck full of explosives into a Syrian army position and detonated it, killing himself in the process. Abu says he was a friend of Abu Hurayra's, and that they "clicked immediately" after they met to discuss their shared ideology.
"He was the best person I have ever met in my life. He had the best character," Abu said. "Abu Hurayra believed this would allow him to go in and kill many of the enemy, including himself. He wanted this more than a bullet. He told me, 'If I go on this martyrdom mission, don't go back to England. Ask Allah to keep you on this path.'"
We asked Abu Anwar what Abu Hurayra told him before he carried out the suicide attack. "He told me to just pray that Allah accepts me as a martyr," Abu told us. "He told me first that he wants this so much and we have many stories of this people who are in these kind of operations, where they've survived the explosion. And on the radio before he detonated the bomb he said, 'I see paradise and I can smell paradise.' This was seconds before he blew himself up."
Abu, inspired by his friend, said he too wants to carry out a suicide attack -- what he calls a martyrdom mission. But when asked if he would return to Britain to carry out an attack, he said no.
"If I come back home, it will be when the black flag of Islam is flying over Downing Street," he said. "I know some people have the intention of come back to do attacks. But me personally, I only have the intention of coming back as a conqueror."
Abu said his family is not aware of his plan to carry out a "martyr mission," but when his time comes to carry out the attack, he said he'll inform them.
For now, Abu insisted that the immediate goal is to establish a caliphate in Syria and Iraq. When I asked if he would now take up arms with ISIS, he said he was considering it. For Abu and others like him, the call to jihad is seemingly too strong to resist.