Make it so that once you have declared war on a tag ,that those 2 tags are blocked, by mechanics of game, from any outgoing/incoming hits to and from any other tag until:
1 Sets end
2 All originals in one tag are dead
If tags abuse it to netgain,then you don't have to worry about any hits from those tags.
If you want to war,why worry about NW finish anyways?
THAT will stop the Team Server abuse.