The situation in the Eastern Plaguelands had deteriorated because vast numbers of undead had appeared there.
These undead had begun rampaging throughout the Eastern Plaguelands.
Tirion Fordring's forces were stretched thin, woefully short of troops.
Tirion Fordring needed troops to defend the eastern coast. The soldiers stationed in the watch towers and garrisons there could not be withdrawn.
If he abandoned the eastern coast, the undead fleet could approach unopposed and begin landing troops in vast numbers. That would create another major problem.
No, it would be far worse than a major problem. If the undead fleet reached shore, landed its troops, and established a firm foothold, that would be the gravest danger of all. Compared with that, the undead rampaging through the Eastern Plaguelands were only a minor threat.
Tirion Fordring had assessed the situation accurately. He moved directly to guard against the greater danger, denying the undead main force any opportunity to land in the Eastern Plaguelands.
At the same time, he strengthened the defenses of Light's Hope Chapel.
Even achieving this much had stretched the combined forces of Light's Hope Chapel and the troops Tirion Fordring had brought with him to their limits. They had enough strength to defend, but not enough to attack.
Light's Hope Chapel could protect itself, but the situation in Darrowshire was rather more dangerous.
Darrowshire was highly unstable, and Tirion Fordring had no spare forces to intervene. Fortunately, Rex had sent both Ulysses and Orys there earlier. Although Darrowshire remained unsettled, it could still hold out, preventing the situation from deteriorating further. Otherwise, the undead could have coordinated an attack from within and without, captured Darrowshire outright, and turned its hundreds of thousands of inhabitants into undead to replenish their ranks.
Reinforcements were certainly needed to resolve the situation in the Eastern