According to Qin Shujian's original plan, he should have led his men directly across the Undead Plain and then launched a pincer attack on the fiend calamity alongside Feiye City.
He simply hadn't expected that the Undead Evil Lord would not follow the fiend calamity into battle, but instead chose to linger within the Undead Plain.
These various factors ultimately resulted in the current situation.
Chapter 51