Above is a link to my rules, helps clean up a lot of blind spots that most rule sets have. For example, it clears up that suggested rule in a way. You can declare war separate from you alliance. You can also request your alliance to stay out of a conflict. However, it does state that wars are against alliances. Otherwise the only purpose an alliance would serve would be to make it take longer for them to be able to declare war. I should add that you have a right to remain neutral if 2 alliances you are in go to war. Review and comment if you would like.