This is sad.
I remember STA fondly for coming to Aztec's help last war, and I don't think anyone thinks this war is personal - it just reflects how the treaty web is currently lined up. Wapa happens to have a history with STA, but I don't think their joining this war, really makes anything personal - they joined via the treaty web.
I'm so far enjoying the war with my STA opponent, who is being a good sport.