When Bai Xiaochun originally made the trip from World City to the Great Wall, he had been with Zhao Tianjiao and the others. Because of the incredible dangers they had faced, their small group hadn't been capable of much speed on their journey.
But now he was traveling through the same area with an army at his command. Furthermore, they had spell formations to increase their speed. Therefore, it was less than a month later that the group of roughly 5,000 cultivators saw an enormous city rising up on the horizon.
It was a city that seemed to abound with murky darkness, and was none other than World City!
The cultivators of the five legions who were camped in World City were there as a backup in case Great Wall City fell. If that happened, they would provide the bulk of the force which would counter attack.