The two most correct posts in this thread. Players need to concede their sense of entitlement. Maintaining good relationships with one civ may well mean having to accept bad relationships with other civ's. The fact that civs form cliques is not a bug, it's a feature. Having said that, certainly a DoW on an unremitting warmonger should not incur a diplo hit, regardless of whether there was a defensive pact or not. Indeed, if it was a sufficiently warlike civ, the other AI civ's shouldn't mind it getting wiped off the map.