The Klingons have had on again off again wars with the Federation though pretty much every series. What would happen if they actually won one of those wars?
I imagine that as long as a race or planet didn't make too much of a nuisance of themselves they would simply subjugate them. For instance, I imagine Earth having a Klingon star base orbiting it and only Klingon ships allowed to land or take off from the planet. Basically saying "No space travel for you, but keep inventing stuff for us."
That and/or they allow people to operate, but under the Klingon thumb. Like most ships requiring a Klingon supervisor on board.
That's all I'm really coming up with so far. I would love suggestions or advice from the forum.