A mobilization involving several hundred thousand troops was naturally impossible to conceal. Too many matters were involved, too many resources had to be moved, and too much manpower had to be redeployed accordingly.
Wang Yan had indeed noticed some of Old Cao's movements, but he had no spies within Old Cao's ranks—not a single one—so there was no way for him to grasp the details. He had only assumed Old Cao was preparing, after the autumn harvest, to guard against an attack from him.
But Wang Yan had in fact considered the possibility that Old Cao might attack him. Even if he had not, large armies still had to be stationed along the border between their territories. With so many troops on the other side, failing to meet them with a properly organized army would have been suicidal.
Fifty thousand troops were stationed in Hanzhong, led by Zhao Yun, Zhang He, Zhou Cang, Guan Yu, and Zhang Liao. To prepare for major warfare and facilitate command, Wang Yan had expanded the establishment: each guard's force had grown from a little over six thousand men to more than nine thousand. Because Bashu's terrain was unsuitable for commanders who charged about recklessly, he had selected generals like Zhao Yun—men with flexible minds and reliable combat strength.
Another fifty thousand troops were stationed in Yang Province, commanded by Lü Bu, Huang Zhong, Zhang Fei, Gao Lan, and Taishi Ci, along with Dian Wei leading three thousand men of the Black Armor Camp. Huang Zhong and Taishi Ci were comparatively steady; the rest were all hotheads. Of course, that was not meant as an insult. Their command abilities were all up to standard, but they ultimately lacked a little adaptability and quick thinking.
There was also the matter of separating Zhang Fei and Guan