Because Shi Kuan, the Demon Emperor of the Northern Lands, rarely attended to affairs, the families there had grown formidable over the centuries. With the advantage of home terrain as well, they had managed to set the pace of the war, forcing Great Shang's troops onto the defensive.
Wang Xin was overseeing the campaign, and he knew that the best way to quell a rebellion was to cut through it quickly. Unwilling to get bogged down in a protracted war with the Northern Lands, he sent out reinforcements.
After sending troops six times in succession, Great Shang had dispatched well over half of its million cultivators to the Northern Lands. Only then did it stabilize its faltering defenses, and the two armies became locked in a war of attrition.
Just as Great Shang was sinking into the quagmire of war in the Northern Lands, Xi Qi saw that so many of Great Shang's troops had been sent there and decided this was a once-in-a-lifetime opportunity. It suddenly rose in rebellion.
The various city lords who had agreed to coordinate with Xi Qi saw it make its move and decided they had an opportunity too. One after another, they joined the rebellion.
Of course, some cities did not rebel. They remained neutral, focused only on protecting themselves, while another group of towns staunchly supported Great Shang.
Great Shang was thrown into a state of disintegration, leaving people across the Six Regions in a panic. They feared the Six Regions would once again descend into chaos.
Moreover, with most of Great Shang's forces tied down in the Northern Lands, it could not quickly and effectively wipe out the Xi Qi coalition. With the help of traitors, Xi Qi instead captured several passes in succession, its forces pressing right up to Hulao Pass.