I should have emphasized the "and", because I know you can have too many wars. You can have too much money. I meant you can't have both of these problems at the same time. And if you do, then start spending that money on getting peace treaties and maintaining them. I never have to deal with more than 2 battles a turn. Many turns in the mid-late game, I am blessedly free of battles. Also...
That's just not true. I have gotten out of several wars, without ever having used Force Diplomacy.