In theory, these airlines have always been at war, but in recent years United has been surging ahead while American has been busy chasing its own tail. Someone at United figured out that if it started to rapidly grow capacity, it could get a whole bunch of gates and American would lose. In short, American keeps growing, United threatens angrily, and American keeps growing again. The point is, United is mad that American isn’t doing what United thinks is rational. So United is going to make sure that it becomes even less rational for American to make those moves.