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This was followed by the creation of the first two Han Banners in 1637 (increasing to eight in 1642). Together these military reforms enabled Hong Taiji to resoundingly defeat Ming forces in a series of battles from 1640 to 1642 for the territories of Songshan and Jinzhou. This final victory resulted in the surrender of many of the Ming dynasty's most battle-hardened troops, the death of Yuan Chonghuan at the hands of the Chongzhen Emperor (who thought Yuan had betrayed him), and the complete and permanent withdrawal of the remaining Ming forces north of the Great Wall.

Where did the Ming armies retreat to?
north of the Great Wall