Hm, well the rough world total military expenditures for 2007 was 1.2 trillion dollars. America's 2008 budget is at least 583 billion dollars, i.e. America spends about as much, but probably more, than the rest of the world combined.

Is America's military more powerful than the rest of the world combined? That's hard to say. But China's larger standing army counts for little in the face of America's air power. Modern warfare is very much dependent upon supremacy in the air, and America is currently untouchable there. Of course, the American military is at the top or near the top in all other categories as well.