For warfare use a two phase "scouts and hammers" technique. First a number of players with very small armies, or no armies at all, scout out the enemy territory. They then report to the players with the large armies, who then coordinate their attacks to the best effect. This can be done with everyone online at once, or with the scouts going out at a specific time, and the larger armies following later. This is a good way to keep all your nobles involved, even when there is not enough money to equip everyone with an army.