They're the "good guys" so anything is permitted. If the chinese or russians would do this, it would obviously be an unforgivable invasion. They'll of course get to chose a good puppet government and adopt a new central bank (priorities) even before getting their hands on the oil. In either case is good that Maduro was removed cleanly from power. Venezuela has been suffering since +30 years from Chavismo that drove them into senseless poverty in such a rich country. It is still not over. Their government is still in power and reorganizing but it was a big step to make changes.