Vanilla probably had one of the better takes on faction tensions. There were plenty of border clashes and fighting over resources, logical reasons for neighboring nations to throw down, but small-scale enough that the leadership could politely overlook these skirmishes as the cost of doing business while focusing on bigger issues like Blackrock Mountain, Silithus, and the Plaguelands. Neither side was obviously evil, escalation happened at a reasonable pace, and even at its worst it was believable that the factions teamed up to deal with the Qiraji and the Scourge.