[dmm]

Yeah, take it to them.

If you're not way ahead of them, they won't surrender. But they might give some planets and/or ships to you if you demand it. Do this enough times and they'll be way behind, and ripe for surrender. But that takes some time, because each demand takes one turn to make and another turn to accept. (And that's assuming they don't just tell you to go soak your head.)

But I think it is always worth your time to obtain a surrender. At least get their homeworld. Glassing them is a waste.