Though selfishness is what chaos is all about, I do not think dibs is a thing...You have already seen two players attack a single province. So I think a stronger province should be attacked by two armies to ensure success. That is from a tactical point of view, because although we are all wanting to improve our -own- characters, I am sure taking the entire planet would mean greater rewards than a single piece of land. So keep that in mind.
Currently working on it and I'm having my forces March south because there be more blood to spill there.