>The "policeman of the world" thing often seems like just a fig leaf / marketing to paper over dodgy stuff. :(

It really is. The US had the advantage of coming out of World War 2 relatively unscathed compared to Europe, as well as the only active nuclear arsenal at the time, as well as every Nazi rocket engineer and Japanese bioweapons expert it could pick up. It basically made the Western world an offer it couldn't refuse - accept American hegemony, military occupation and generous loans for postwar reconstruction or flip a coin on whether Washington or Moscow nukes you into atoms in the great game of superpower chess that would define the 20th century.

It isn't hard to look at American foreign policy as being little more than a shakedown operation.