I got the Papal States into a war against the Moors last night, and I didn't ask them. A Moorish navy was sitting next to a Papal fleet when I attacked it. I allied with the Papal States early on in the game. Two allies adjacent to the same attacked stack=assistance in the battle. Therefore, the Papal States was now at war with the Moors. I attacked a French fleet in the same way, and the Papal fleet assisted there too. The next turn the French were excommunicated.