Robert wrote:

I understand now!
Middle East issues became very clear to me after some drinks: let me explain !
We support the Iraqi government in their fight against IS. We don’t like IS, but we are ok with Saudi Arabia, who is supporting IS.
Also we don’t like president Assad from Syria and we support the fights against him. IS is also fighting Assad but we do not support IS.
We don’t like Iran either, however they support Iraq fighting IS.
So, In short: some of our friends support our enemies and some of our enemies are fighting against our other enemies. We want our enemies to lose but we don’t want our enemies fighting our enemies to win either.
When our enemies, who we want to be defeated, are defeated they are most likely to be replaced by people we like even less than our enemies.
And all of this started by us invading countries to fight terrorists who weren’t actually there until we went in there to drive them out.
Questions?

I believe this is what Henry Kissinger called "détente ".