You might be able to issue certain edicts in any population, even your own, which puts a segment or the whole of the population in something akin to slavery. Forced labor, strict food rationing, basically no self determination. Of course, to prevent open revolt in most species and cultures, you might have to have armed guards all the way down to shackles. Mass indoctrination, if you don't want to have to watch the buggers every minute of every day.