The u.s. Army/navy/Air Force is second to none and I bet they could easily beat the armed forces of any other country on this planet with the possible exception of china or Russia.  

However, and as we've seen, winning the peace is a far different thing, and they've been frankly horrible doing that.  After 16 years Afghanistan is slipping away, and Iraq isn't much better.  

I like to think the u.s has learned from these examples but that those who do not understand history are doomed to repeat it.