Well, in the case of Venezuela, they don't need to start positioning aircraft carriers and/or troops. The covert operations we've got going on over there are doing an excellent job of destabilizing that country and ripping its democracy out of the hands of the majority of its citizens (in order to gain access to its oil, of course). We don't just do overt wars. We're also quite adept at gaining dominence over other countries using other means. Bear in mind that I said "world domination" and not "world conquest".