He who knows pain is dangerous, as he burns within for revenge.
-- Till Lindemann
In the beginning of the 20th century, there was Europe, the Americas, and other countries which belonged to one of the first two. In Europe, an elaborate system of alliances was established, on the grounds that this would prevent the horrific wars of the previous age, the Napoleonic.
But in the massive Austrian empire, numerous groups yearned for freedom. Sure, Austria shared its crown with Hungary, but it also contained the various groups of the Balklands, who had no representation in this government. And one of them made a point of shooting the heir to the throne as a big middle finger to the monarchy.
Austria blamed tiny Albania for this, and war was mutually declared. In the modern world, this would probably been the end of it, but each side pulled in their alliances. Which pulled in their alliances. And the next thing anyone knew, pretty much the entire world had been sucked into it. This was World War I.
World War I proved so horrific that everyone assumed that it was the last war to ever happen in history. It ended with victory for the Entante of the UK, France, Russia, and the United States. The Central Powers of Austria, Germany, and the Ottoman Empire were totally destroyed, with Austria split up into its component nations, Germany losing large amounts of land to its neighbors, and the formation of Poland out of its borders. The Ottoman Empire was completely destroyed, shattering into some hundred minor countries. The Entante suffered quite a bit as well. Germany had snuck deported radicals back into Russia, leading to the collapse of its government, and the establishment of the Soviet Union in its place.
Between losing the war, losing international prestige, losing loads of land, and being fined obscene sums of money, Germany and Austria seethed inside for revenge, which pretty much lead directly to World War II on the European side.
So when the Allies won World War II, they learned from this lesson of history. The defeated Germany and Japan were not punished or fined in any way, over Dutch objection. The US passed the Martial Plan to rebuild the ruined Europe, fearing the influence of both internal radicalism and hostile foreign powers like the Soviet Union.
In the modern day, the US is in two wars. One with Afghanistan, one in Iraq. The old governments are mostly defeated now, but the rebuilding proves difficult. Both countries have resistance movements bent on sabotaging the whole thing. In Iraq, there is both the remnants of the old government, and an "Al-Quida in Iraq" that sympathizes with the (dying off) terrorism movement. Both are practicing asymmetrical guerrilla warfare, which is a very very difficult tactic to counteract. The "guilty" blend in with the "innocent." Any attempts at purges generally only strengthen the resistance movement by encouraging recruiting. In Afghanistan, various warlords jockey for position, some are in favor of the US plan, but others sympathize with the old government, or see themselves as a potential great king of Afghanistan, and want to defeat us to make their goals happen.
While it is possible to defeat an asymmetrical opponent, it is a massively frustrating process, and none of the traditional markers of warfare apply. One must be more police officer than warrior, more social worker than bomb thrower. One must work with propaganda, not only to look good, but to have as much as possible have it backed by fact.
And ultimately, wars must end. War makes military recruitment more difficult, costs boatloads of cash, makes people die, and generally drains national resources.
I'd say that the two wars are 95% done, and we should avoid starting another one. We can join another one if alliances demand, but ultimately this should be the time to withdraw, retool, and rebuild.
Also, the war has made a number of interesting effects. The US is badly in debt, but the Iraqi government is riddled in money. Perhaps they could buy US bonds? It would be a good reason to end the war, especially if more "kickbacks" can be had in the future.