You can't actually break (right-click, remove) alliances during WoE, if I recall correctly, have you ever tried it?
The thing these people do is keep their antagonist list open, and switch them over there to "break" alliances.
Though I disagree. It's your responsibility to have allies that will STAY allies. All about strategy. Why would the system stop betrayals? Stop, or prevent them, yourselves. It's gonna be on their name too. "Blahblah guild is known for turning on allies." Then in the future, don't ally them, nor trust very easily. As much as it would "hurt," hello, RO is just a game. (zomg flames coming!!!11)