Obviously, the NPCs couldn't have failed to perceive the overall situation. However, even if they had anticipated the unfavorable development of the circumstances, there was nothing they could do. They couldn't limit Zhou Tian's party from flexing their might because they lacked excess strength. Aside from using all the power they had at their disposal, the NPCs had no other means to rely on.
As a result, under such conditions, with Zhou Tian's party exerting themselves, the NPCs defensive line began to steadily shrink, and Zhou Tian's bearmen started making incremental inroads into the enemy's defense line.
Presumably, unless something unexpected happens, even if the NPCs were to resist fiercely, they would not be able to prevent Zhou Tian's invasion. Once Zhou Tian's bearman breached into the city, the castle would inevitably fall into Zhou Tian's hands.
