Technically speaking it's our war.
When we conquered the middle east in WW1 we took large swathes of it from the Ottoman empire. These had existed as provinces for centuries without much strife between them. We then carefully drew the borders to ensure that each new country had a good mix of groups, so as to play them off against each other.
The Kurds are a great example, instead of being in the logical "Kurdistan" they got split between Iraq, Iran and Syria. We considered them a threat to our interests in the region and wanted to neuter them. The official intelligence reports from the era, now declassified, are quite blatant about this. Laurence of Arabia described it as "a state of political mosaic, a tissue of small jealous principalities incapable of cohesion".
The final part of this duplicity was setting them up against one another. Typically we'd select one of the smaller minorities and give them arms and money so as to rule over the other. Saddam is a good recent example there, he's of the Shia sect who are the minority in Iraq. We taught him how to torture and propagandise people and even went as far as helping him to gas his opposition.
Iraq is unstable literally because that's the way we intended it. It's operating exactly as designed.
When we recently invaded Iraq for the forth time in 100 years we switched things around. De-Baatication laws were passed by our collation giving supreme power to the Sunnis. All Shias were entirely banned from any form of government service, from being politicians right down to being lollipop men. The Sunnis, pissed off after decades of Saddam, then took their revenge on the Shia regions where they now controlled local government, the police and the army. Essentially they operated as an occupying force, you can guess how that went. As allies of ours this of course was not widely reported on our media.
Ultimately this is why ISIS has so much support in the north west regions of Iraq. Us helping the formation of ISIS in Syria is merely icing on top. But the cheery sitting proudly at the peak has been how we've managed to get our own population to believe that this is all down to fundamental character flaws of the people in the region when the simple reality is that it's a proxy war we created and nurtured for a century entirely for our own strategic benefit.
tl;dr: stop hitting yourself
