[ericthered]

secretly trigger a nuclear war, let human society collapse, and then mysteriously appear, let human governments take the fall for the destruction and commandeer the rebuilding effort by making the invaders look helpful. Earth won't recover for a few centuries, but we're patient, remember? I'm not sold that this is the best way, but its an interesting one.

Less dramatically, I'd partner with power hungry and easily controlled pawns to do my dirty work and provide grunt forces. "Invent" a few things, and grow rich in the local currency. Start funneling economic growth to a nation I feel I can control. Build everything up over a course of a century or so, then engage in normal conquest. Hopefully after I've managed to trigger a civil wars in the largest countries.