The title already gives you a hint what I'm looking for, ideas of game systems that encourage players to go to campaign where their alliance is currently loosing on the map, i.e. all objectives are owned by the enemy. Of course it works vice verse as well, meaning ideas that discourage players to go to campaigns that are completely taken by their faction are just as welcome. It doesn't necessarily have to be about the psychological aspect only, ideas of simple changes to the gameplay that favour balanced campaigns work as well.
Note that this is only about the current state of a map and how to keep it interesting for everybody at any point in time, so anything faction scoring related doesn't belong to this thread.