Actually, there arent a lot of armed forces in any 1st world states that would be capable of really achieving what the US forces were sent out to do.
The basic mistake lies in the premise of fighting an aggressive territorial war, but afterwards wanting the conquered territory to stabilize itself.
The main problem I see today is that the USA are too quick to throw their military at problems, when they havent got a real plan or idea thats feasible. Shoot first, ask questions later doesnt work (anymore), and while most european countries, for example, dont have much better answers either, you can see they are getting more and more cautious about getting involved into such things.
Slightly sidetracking, the last somewhat successful modern military action has been the kosovo war. I was in the german army during that time, and I can assure you it took a lot longer, and required a massive shift of tactics halfway through to adapt to the situation of elements of the populace fighting you, rather than an army.
Also, as the article about 4th generation war states explicitly (and I hereby distance myself from this school of thought. I think talking about generations of war is far too generalistic and dangerous) the western forces are usually not prepared to deal with several moral issues. Frisk muslim women for fear of suicide bombers? Lose-Lose here. Either you frisk them, and quickly have a massive uproar about violating social etiquette and culture, or you dont and get blown up.
Same with the PoW issue. The whole "Rules of Engagement" type of laws were created with the war between state armies in mind. By that law, a random partisan doesnt have the right to become PoW, which is actually a state that grants a lot more protection than just being imprisoned in Abu Ghraib.
Then, you got the problem of soldiers misbehaving, and due to the disconnect between leading echelon and the grunt, very little repercussion.
A single shootout in a population center where german soldiers misbehave and slay innocents out of spite will do more damage, and cost more lives for both sides, than most political mess-ups on TV or behind closed doors.
In the end, right now the western world isnt equipped to deal with this kind of warfare in a satisfying manner, which makes the USAs insistence on engaging in such conquests all the more tragic for the guys in the field.