There are a lot of inactive players in PvP and they have a lot of their base claimed.
Suggestion: When a player has been offline for at least 2 weeks, they should lose 1 power every 12 hours. (Total power is 25, so if they are at full power, it will take 12.5 days (just under 2 weeks) to lose all power.)
So, if a player is offline an entire month (~4 weeks) they will be completely drained of power.
At the moment I think this would be sufficient to provide some raiding opportunity within factions and to encourage people to stay semi-active during off peak periods.