Does anyone really believe that America's leaving Iraq will improve the situation there? It will create a power vacuum; the insurgency will get stronger; the Shia might retaliate against Sunni violence, setting off a civil war, and the Kurds could be tempted to secede. Iraq would then be exporting terror and instability. Some Americans might say, "That's fine, we'll be gone." But any withdrawal will take months, during which the violence will mount. The last American forces to leave under these conditions might not get a more ceremonious exit than they did off the embassy roof in Saigon in 1975.
Remember those often-cited studies that said having a large force to secure the peace is crucial in nation-building? Well, all of them point to another, perhaps even more important, requirement for success: don't leave. During the 1990s the places the United States and its allies left—Haiti, Somalia—were failures. The places where they stayed—Bosnia, Kosovo, East Timor—have been relative successes. Look at Afghanistan. It's faring decently today, but were foreigners to leave, it would almost certainly regress, probably into some kind of failing narco-state.
But why take Zakaria seriously, you ask, he's just an armchair-columnist. Well, ok. Let's take a head of state then. Hameed Karzai, in an interview with India Today, says:
The US presence is essential for Afghanistan's stability. The US helps us a lot to fulfil our desires. We visited the US for 5-6 years during the Taliban rule for their support. Now without the US or international presence, do you think three million refugees would come back? International presence in our country is extremely important. [...] Till Afghanistan stands on its feet and has its own economy and education capability, we will need help from the US and the rest of the world. [...] As for the outside forces, if they leave Afghanistan may go back to chaos.
Ditto Iraq, wouldn't you think?
(The India Today site is only accessible by print subscribers, and they require you to key in a four-digit code to enter. My advice: try out a few!)