Well, the basic idea is that some inhabitants of colony A may figure that if they remain on A, they can only expect to get 100 resource units, but if they move

Well, the basic idea is that some inhabitants of colony A may figure that if they remain on A, they can only expect to get 100 resource units, but if they move to B, which is weaker, they may be able to acquire 1,000 resources units instead. They wouldn't bring back resources from B to A, they would just do a hostile takeover so that they can live like kings.