So I did a quick google search and found this from yahoo answers
How true are these statements?The U.S. Navy and Air Force, along with various units of the Army and Marine Corps, have virtually all of the world's power projection capabilities - the U.S. military can literally project power almost anywhere in the world at short notice (which is not to say that the U.S. might not pick an opponent too strong to win an overseas engagement with - China, for instance, is too strong to invade - but the U.S. could land troops almost anywhere in the world - say, a raid on Hong Kong).
The U.S. Navy and Air Force are, in fact, as powerful as every other foreign counterpart, combined - I believe that, in a war against the entire world, the U.S. Navy and Air Force would each be approximately equal to the entire strength of the rest of the world in the air and on the seas.
As for the U.S. Army, it is one of the largest in the world, as well as one of the best equipped, well trained, and experienced - all at the same time. No other country can match this - other countries are just as big but lack modern equipment or training (China, India), while other countries are as well equipped and trained but lack the size (Britain, France). Most other countries also lack the massive logistical system that backs up the U.S. Army and the other armed forces - who else operates almost 100,000 trucks, plus another 100,000 utility vehicles, to support the soldiers in the field?
Basically, no other country can maintain sizable fleets in Japan and the Persian Gulf while also patrolling the Gulf of Aden and operating in the Atlantic, Pacific, and Indian Oceans, and still having a sizable force at home on leave or in maintenance. No other country can decimate even a reasonably-sized air force and C4I system from the sea.
No other country can bomb any spot in the world from bases at home for weeks at a time, maintain fighters in various bases worldwide, transport thousands of tons of equipment and supplies worldwide, daily, and watch the entire planet from satellites while also being able to deploy aircraft for a closer look when necessary.
No other country can fight two major wars at the same time in different parts of the world while also remaining capable of fighting a third (Iraq, Afghanistan, and North Korea) and still having a reserve and the ability to rotate soldiers back home for rest and training, and the ability to send soldiers for surprise operations anywhere worldwide.
The U.S. military can do all that. It can't invade China in a war of conquest, sure, but it's not designed to do that because there's absolutely no need, and no one else is capable of coming close - China would have a hard time invading Taiwan (maybe they'd win, maybe not), Russia had difficulty knocking Georgia out back in 2008, Britain and France can deploy a few thousand soldiers rapidly in Africa or the Middle East but they can't get much bigger than a division on their own, etc.