Who owns the moon?

[JKPolk]

If you do first come first serve, then who's to say "you can only own x amount of the moon?" And why shouldn't America simply use the argument that since there's already an American flag planted, it's our moon? Obviously because these would result in massive retaliation from neighboring countries. First come first serve would only result in a violent race with lots of subterfuge and could easily result in massive territorial wars both in space and on earth.

Also I mentioned that plans are already nearing completion for lunar bases, which will have construction begin in less than 5 years. These laws are going to come into light very soon.