C1020 War
Once the Witch Clan retreated, the Devil Clan and the Shadow Clan wouldn't be able to defend against the Heavenly Tao Alliance. They would be slaughtered.
Although they were allies, everyone had their own plans. No one knew what the people of the Witch Clan were thinking.
If they really went back on their word, then the Devil Clan and the Shadow Clan wouldn't have to fight anymore