Many people here are thinking simply along the lines of military might. Thinking outside the box, however, leads you to see several grave weaknesses for America.
1: America is network centric. With all the benefits this brings, it also means if someone got a few missiles into space, our country descends into absolute chaos, while other, most likely analouge-based countries, will not nearly be as effected.
2: America may be physically strong, but as to be observed though its last several war attempts, its will...is not so iron. If the aggressor are wise enough to think about it before hand, a massive propaganda/psychological warfare campaign, using the American media would be devasting to morale and the war effort.
3: Prryhic Victories. Our enemies may be willing to completely sacrifice their existance just to harm America - they may be destroyed, bu so long as America is forever changed because of it, they've won.
4: Who we're fighting. Though most of these posts assume an Eastern aggressor, like China or Russia, many of them don't think of what would happen if say, we pissed off the EU. Or Japan. The EU, Japan and several our allies hold resources and supplies vital to the American war machine. Loss of these supplies would be devastating. For example, the EU holds the only factories in the world capable of producing armor for the US' MBT, the Abrhams and the armor used in several other vehicles, like the Bradly, as well as the only other factories capable of producing the barrels for these vehicles. Most of America's electronic advancements have come from Japan, such as EMP shielding, and most recently, much of the electronics that make our air superiority possible, like with the F-22 and F-16. Ireland is another example, being the world's current leader in producing high-end electronics, much of which is used in the US military.
This isn't mentioning the fact that many countries in the EU, and in Europe in general, are usually considered to have something over the US in terms of military power, such as with Britian, who is generally regarded as having the world's most effective armor, and the world's best trained and equipped infantry. (Most estimates make it to be that upon completion of training, the average British solider is has recieved 4x as much training as the average American solider, and that their equipment is generally far more effective and reliable then our own.) France and Britian are usually considered to have the best special forces (with America following in a close 3rd, admittly), while the makers of some of the world's most effective weapon's systems are in the EU - Germany is one of the best.
Naval Power and Air Power are generally still considered to be America's field though, which is fortunate, as it is what keeps us safe. If any of you remember the incident with China, where one of our C-130's crashed on Chinese soil, reading the reports filed after that, the lead negotiator remarks on how several Chinese officials stated, quite boldly, that American air power was the only thing keeping them safe - that if wasn't for that, America would be crushed by now.
Then again, I guess China can make those kinds of claims, seeing as how even the US's most conservative estimates put the number of women in the Chinese military alone as equal to or greater then to the total number of US Armed Forces combined.
Lets hope no one in charge over there in China ever decides to play as the Zerg......
