This is just a simple trick with diplomacy you can use. Mainly, if you brought a few civs into a war against a common foe, you allies will likely continue the war due to the success. However, you are paying a hefty price for that alliance, thats why you should end the alliance after 20 turns. However, after ending the alliance that you are paying for, start a new alliance and ask money from the AI. This will help you recover some of those gold per turns that you lost in the alliance, it will slow you allies' advance on the dogpiled enemy, and this will give you more power to conquer/burn and pillage more of the enemy's land before your allies. I've been using this strategy ever since I understood the diplomacy rules of civ 3. I havent seen a post about this so I apologize if this is a well known strategy already.