How about this.
You can only claim one chunk in the beginning as a faction.
There are upgrade options in which you spend points.
To claim another chunk, it costs 1point.. And then 2 and then 4 and then 8.. Etc.
If you kill someone, you get a point. If you kill someone you are at war with, you get two points.
If you kill the faction with the most points, you get double points.
Catch.. If you declare war, you can't undeclare for 1week.. And you lose equal points each time you die as if you would claim them.
This way, the top faction is always at risk because everyone is after them and claiming land is a luxury.