It's pretty important to remember that most of the US's more notorious military actions consisted of small Special Forces groups.
The US military is built around the "fleet in being" principle, where the very existence of the military means it will never be needed. There's a very good argument to be made that the US's "10,000 lb gorilla" status is why there hasn't been a major war since Vietnam, Korea or WWII (depending on your definition of a "major war"), and that the latter two (Vietnam was a French colonial war that the US felt they needed to clean up when France got kicked out) would never have happened if the US had bothered to maintain a real military in the first place.
The world of 2014 isn't much different in terms of trade patterns, international movements, and such (all the reasons why people claim there will be no longer be a threat of real war) from the world of 1914, with the only real difference being the rise of the EU (the long term effect of which is too soon to tell) and the complete lack of an international armaments race.
The idea that "conventional warfare is obsolete" very well stem as much from the fact that most of the US's allies shelter under the US umbrella (rendering an arms race unnecessary and allowing them to restrict military spending to just enough for immediate self defense) and that most of the US's potential enemies are so far behind the power curve that there's no way to catch up (rendering an armaments race impossible). There's at least a dozen areas where full-scale regional warfare could easily break out due to serious tensions between neighbors at any given time, and there's been a few situations over the last few years where I still am not sure how war didn't break out.
Meanwhile, the Pax Atomica has flaws, as no nation is going to resort to nuclear weapons unless they're involved in a total war to begin with (the things are just too nasty), which is why the US abandoned the "nuclear army" mindset during Vietnam. Now, the rise of laser weapons and super-accurate ABM missile systems means that even the "unstoppable" ICBMs are no longer guaranteed to get through, weakening the deterrent effect further.