SIMPLE SOLUTIONS TO WAR
1. Both leaders online.
2. An amount of players on the defending and attacking side such as they have to have a certain amount of players to attack them.
The current war rules don't seem right you can't really ambush and it will just be a shitload of Metagamming. I once played on a nations server that had these rules, etc there needs to be 7 players in the town/settlement your attacking.
Yes, this is stupid simple but it worked very well.