pvp you would have a high drop out rate server would die within a week join a tribe and attack no tribe wants war because it would lead to a server merge
I am not sure that PvP per se will cause players to drop out in high numbers. But if one LARGE Tribe does dominate a server then there is an opportunity for players to drop out. Even a small v GOOD Tribe can cause problems as happened in the MAYAPAN Server but there the issue was that this ONE Tribe knew the game battle mechanics better than others having played on another language server that had been running for longer. It really is upto each Tribe to keep their Tribe cohesive but often what happenes is that each player is too busy looking after themselves that they dont see the bigger picture until they get up the ranks.
One ahs to give thjis game to develop a bit more and see where it is headed to see what the outcomes will be.