They aren't, but they just can do that. International politics is reallllly anarchistic because how the fuck do you arrest a country. Say if the U.S decided to just stop exporting anything at all- no more food and other stuff- all you could really do is just tell them pwese downt doo that, we need the foweign aiwd :3 This also assumes your the leader of a powerful country, which is a rather difficult position to get to.

In essence, get fucked international politics go brrrrr