The players were following after Dave, this time respectfully accepting his commands and orders. He didn't ask to be listened to or asked to become their commander. But the discipline the undead army showed to Dave had affected the players.
They walked behind Dave's undead army in an organized manner and aided him in liberating all the possible areas of the desert. As for when the Blue and Green Qin units showed up. All had understood that they weren't capable of pushing them back and were forced to change direction.
Dave spent an entire in-game day in liberating the southern desert. But he never was able to push back the blue and green units. They were too powerful. Yet thankfully, these units only acted as a barrier to prevent Dave from retaking more of the Southern soil. These units didn't advance to the other oasis, or all of Dave's hard work would have been for naught.