After WWII we did occupy both Germany and Japan. There was a concerted effort at an insurgency in Germany. However, it never got off the ground for several reasons.

1. We kept about 300,000 troops in Germany and declared martial law. This kept peace and squelched any major resistance while the country rebuilt and establish the new government and security forces.
2. We also rebuilt the economy and infrastructure to some degree of self sufficiency.
3. We didn’t leave till the basic foundations of government, security, and economy were up and running.

When you depose of the government and infrastructure you are left with a power vacuum. If that’s not replaced with something comparable then you have chaos, as in Iraq. If we followed a model similar to Germany or Japan after WWII and yes, left at least 300,000 troops in there to administer marshal law while will rebuild the infrastructure then it would and still could work. And no, the armed forces are not stretched too thin. Yes, it would be tough, but very doable in the sort term; 3-5 years as in Germany. US armed force total call up of regular forces and reserves is about 1.2 million… If we had left 3 or 4 hundred thousand troops in Iraq from the beginning secured control and secured the borders from interference from Iran and Syria, we actual be starting to bring them home NOW for good!

We, as a country, have become spoiled, lazy, and complacent. Expecting instant gratification from anything we do. (Just like the later Roman Empire)
We only look at the short term results and not long term consequences….

Rumsfeld should have been fired 3 years ago, as soon as things began to go wrong. It was a gamble to think that the Iraqis would step up like we hoped.They are more loyal to their religion than their country. What we have now in Iraq is our own fault for trying to do things on the cheap and be TOO nice…

Ultimately, West Germany didn’t disintegrate into insurgency because we could focus them on the USSR. But, it could have easily gone that way once they started to recover. The biggest difference was that the infrastructure of Germany was destroyed and the people pretty well defeated. We did NOT do that to Iraq, nor do they have an external enemy to focus on that the US can help them against. Well, they do, but we haven’t played it that way.