I honestly don't know where some of you get your "information" from. ISIS existed in Iraq during and after the invasion but it was essentially just a band of extremists that were contained by the Sunni tribes and they were mostly social media jihadists. They didn't control or occupy any actual land and they weren't slaughtering people and destroying civilization for ethnic minorities.
That all changed when that country next to them, known as Syria, became a civil war wasteland. This same country just happens to share a massive border with Iraq. This same country also happened to devolve into complete anarchy which allowed this previously clawless Jihadist group known as ISIL to use the ungoverned land in eastern Syria to organize, recruit, arm, and fundraise.
From there ISIL saw recruits pour in, they armed them, they lured in ex Iraqi commanders, and they then poured over the border. What awaited them were totally unprepared Sunni Iraq troops that didn't consider the prospect of having to face radicalized fanatics with a scorched earth policy. So they fled.
So really, it was the lack of intervention from ANYONE in Syria that created the completely ungoverned territory that ISIS quickly assumed as their own. They assessed that the US wasn't going to intervene, nor was anyone else, so they set up shop with almost complete assurance that they weren't going to face an organized assault from a military worth a shit.
And now we have what the French Defense Minister correctly stated today, a full blown well organized terrorist army. Enjoy.
