The Islamic State of Iraq and Syria (ISIS) seemed to come from nowhere as it grabbed territory in Iraq and Syria.
But where did it start?
CBS News traced ISIS back to a U.S. military prison.
Camp Bucca was known as the largest, and one of the toughest, American prisons in Iraq.
As a vicious insurgency raged across the country, Bucca's numbers swelled.
But there is growing evidence that the sprawling prison was also the birthplace of ISIS.
According to a CBS News investigation, at least 12 of the top leaders of ISIS served time at Camp Bucca, including the man who would become the group's leader, Abu Bakr al Baghdadi. CBS News obtained photos of 10 of them in Bucca's yellow prison jumpsuits.
At the time, few predicted that Baghdadi would become one of the world's most wanted men. He spent 10 months at Camp Bucca for an unknown crime. But during his time there, he would have rubbed shoulders with some of the most dangerous Islamic extremists.
"I think it's undeniable that one of the main causes of ISIS's explosive growth after 2010 was Bucca. It's where they met, it's where they planned," said Patrick Skinner.
Skinner is with the Soufan Group and was a former CIA case officer who spent time in Iraq.
"Everybody could see what was happening but nobody could do anything about it," Skinner said.
U.S. officials who worked at Bucca told us they were concerned that prisoners were becoming radicalized. The prison has been described as "a pressure cooker for extremism."
And that wasn't the only problem. It was at Bucca that an unexpected and powerful alliance was formed between the Islamic extremists and the Ba'athists loyal to Saddam Hussein, who were angry at losing power.
"You put them together and you get a mixing of organized military discipline with highly motivated, highly active ideological fervor, and the result is what we see have today," Skinner said. "I mean, there were other circumstances, but the toxic brew of Bucca started this recipe."
The U.S. set up a rehabilitation program at Bucca to try to combat extremism, but some who worked there have said that it wasn't implemented effectively.
At the time, Iraq was in a state of complete chaos. There were 100,000 prisoners in the country, and the U.S. was completely focused on the insurgency -- they weren't necessarily thinking of the future.