What are the 10 major USA allies and 10 major USA enemies?

So say there is another World War (ya know N and S Korea) and there were going to be 10 major countries on each side, what countries would be with the USA? Ive seen stuff about the "NATO" or whatever but if you are going to mention it, please explain what it is cause im not really sure. So just what are the 10 major allies and enemies and please only countries that would actually fight in a war with or against us.