The most obvious course of action, after securing a magical base of power, would be to suborn governments that, like the British wizards, are largely controlled by a very few people. Mind control, though an easy method, wouldn't necessarily be required or desirable to do so. Building up a muggle nation in Africa or South America would not only present few magical signs to the outside world (wizards would likely ignore it as they do most muggle things, while muggles would simply view it as the actions of a very successful warlord), but would pose little danger to his power bloc if things went wrong.