The battle was firstly triggered by the Left King's Palace and the Desolate, when they fought over a piece of land. Then the war spread, finally involving all other countries in the world.
It was hard to imagine that the Left King's Palace was the first one to exit the war. It had the least amount of losses during the war and with the support of the West-Hill Divine Palace, it had retained most of its strength.
With the dust behind them, thousands of cavalries marched into Yan territory. They claimed that they were going to overthrow the Tang Empire in the name of Heaven, which in most people's eyes was quite a poor excuse.
Most people believed it was because Long Qing had taken full control of the Left King's Palace, and he was back in Yan Kingdom to seize what was supposed to be his, including the throne.