Planet Subjugation and Protectorates

[Saxon]

If memory serves, it is all about score. If you have six times the points, you can set up a protectorate and eight times the points, you can have a subjugation. Ten times the points gets you surrender. I have not played with it much, but it seems a fairly straight calculation. A decent move is to hit their fleets hard right before you ask, as the number of ships is heavily reflected in their score. They lose the ships, they drop below the points threshold and they are yours.

I also think this is why a lot of people do not like playing PBW with neutrals. They are too easy to pick up in mid game and usually give a 9% boost to the empire that makes them surrender. As it is probably the player in the number one spot, it just opens up their lead for no real work.