I hear we've been in Iraq for almost four years now. People point out that that's longer than our participation in WWII. Interesting.
During WWII the US pretty much destroyed the significant German cities, destroyed its military, and got rid of all of its political structures. It took just over three years to accomplish this. The war ended in 1945.
The last time I looked, we're still have a vast number of soldiers and bases in Germany and Japan. That means we've been there about 60 years.
How about Korea? I guess we're still there, too.
How about Bosnia/Kosovo? Yup...still there.
It took us 3 months to win in Iraq instead of 3 years and we didn't have to drop any nukes on them. Now, just like Germany and Japan, we're engaged in the rebuilding phase and we have some 50-ish years to go.