《明史·列传·卷八十六》
后来又从东胜撤防，驻守延绥，河套地区就这样丢掉了。
后又撤东胜以就延绥，套地遂沦失。
Later, they had again withdrawn from the defenses of Dongsheng to defend Yansui, and the Hetao region had been lost. 
<s>[INST] Kindly elucidate the central themes in this passage in English: 后又撤东胜以就延绥，套地遂沦失。 [/INST] Later, they had again withdrawn from the defenses of Dongsheng to defend Yansui, and the Hetao region had been lost. </s>
Kindly elucidate the central themes in this passage in English: 后又撤东胜以就延绥，套地遂沦失。
user
Later, they had again withdrawn from the defenses of Dongsheng to defend Yansui, and the Hetao region had been lost.
assistant