In my opinion, by establishing a new world for a temporary period, an equal number of castles and soldiers can be given to those who will actively participate in the game and who want to fight, so that they can practice war among themselves.
At the same time, the war can be sustained by giving the option to buy soldiers with gold to those who lost all their soldiers here.
Of course, this new world should not affect the real crusade world and should not give it an advantage.
Players in countries where there is peace during the temporary protection process do not break away from the game and do not get bored. This idea and buying options with gold can be developed by you.