This has been a managed political war from the start. Early on, Bush had the US stand down in Fallujah for a month for no real reason, I think it was some UN bullshit. Who wants to fight wars that are managed by the UN? So after a month for the Iraqis to fortify we had a hall of a fight there when we easily could have rolled up the place in a few days. That's just a head's up on how things work. I lost interest in the whole mess at that point, 'sides, if the same factions have been killing each other for 1400 years why try to make them stop now? I'll go with the former Gov. of Alaska on that mess: "let Allah handle it!"
Our intervention, whether it is in Syria, Ukraine or Iraq, is justified only if vital US interests are at stake and if the Congress duly approves the use of force.
Liberals and a fair number of pretend conservatives seem to only want to intervene in situations where we have no vital interests. Nothing to gain and plenty to lose, at least for the poor joes who get sent in there to risk their lives so some pol can have a talking point.
I am sick of being lectured by people about the so-called "lessons of history", which are said to dictate that we must confront evil everywhere it rears its head or risk world war later. History teaches no such thing. I can list dozens of counter examples.
The same neo-cons who demanded an attack on iran now want us to implicitly be allies with them against the sunni terrorists. We installed this Maliki character in Iraq. Now he is no good. Same with Karzi in Afghanistan. Maybe the real lesson is stay out of situations we have no business in or no understanding of.
The other obvious lesson of history is that peace and stability in the islamic middle east are brought about authoritarian governments. Egypt, Syria, Libya, Saudi Arabia, Saddam-ruled Iraq, Iran, et al, all were relatively stable under traditional arab strongmen rulers.
Of course that wasn't good enough for us. Bush and his cluless neo-con advisors wanted to force western democracy on countries with no history or tradition of it. Obama went even further and openly supported islamist groups tied to al qaeda.
As a civilized western country hamstrung by various interantional conventions on the rules of war, we are singularly incapable of dealing with these insurgencies. Saddam would have surrounded Fallujah with artillery pieces and reduced it to rubble. Problem solved. We thought door to door fighting was a better option, with the predictable horrific causualties. Of course, none of our pampered philosopher king generals or preening pols was kicking in doors, so what did they care?