This is not because the US is the big dog in the world (well okay, that's a factor, but not the main factor). This is because these things are always reciprocal

This is not because the US is the big dog in the world (well okay, that's a factor, but not the main factor). This is because these things are always reciprocal cooperation agreements. The US goes to Canada (or some other country) and says "Hey, if you'll help us enforce our embargoes, we'll help you enforce yours." And the other country says "Deal!" EDIT: Above is the carrot. There are also sticks that can be brought to bear, like import tariffs.