"The song is very simply about war. Us and them is referring to the sides of the war."God only knows its not what we would choose to do" is saying that he knows that both sides don't really want to be in the war. "And who knows which is which and who is who" is saying that everybody, in the end, is the same. and there is really no point in warring with each other. Some of the stuff i have said may be a tad innaccurate, but I'm only human. This is the general concept of the song, though."