It’s a new habit of alliances who have no chance to win the war and want to loose fiefdoms. All but a few members will be kicked or leave the alliance. The alliance is eliminated from war an the fiefdoms will be randomly redistributed. So you can loose the war in the first minutes of the season, if your hardest opponents get the additional fiefdoms. Or you can loose the war in the last minutes also.
Please find a better solution. I will quote a suggestion from a different thread:
The easiest solution would be to leave the alliance in place and just take away the possibility for members to attack (and set the skulls to zero). So you can beat them no matter what and the fiefdoms won’t be randomly redistributed.
Although you must give a different solution for alliances that cease to exists. But in this rare cases (only with very small alliances) the old solution would be fine.
EDIT: Oops. Better category would be “Suggestions & Improvements”???