C1144 They Turned into Spears

Why was it that from a macroscopic point of view, this was a bad move?

The reason why the North Territory had been in trouble repeatedly was that the Heavenly Demon had clashed with the North Territory, attracting a large number of the living forces of the North Territory, and thus neglected the supervision of the back. This caused Shadow Demon Xu Yan, the Outcloud Imperial Dynasty