Query: What group did the Manchus take over to add strength to their numbers?
Context: There were too few ethnic Manchus to conquer China, so they gained strength by defeating and absorbing Mongols, but more importantly, adding Han Chinese to the Eight Banners. The Manchus had to create an entire "Jiu Han jun" (Old Han Army) due to the massive amount of Han Chinese soldiers which were absorbed into the Eight Banners by both capture and defection, Ming artillery was responsible for many victories against the Manchus, so the Manchus established an artillery corps made out of Han Chinese soldiers in 1641 and the swelling of Han Chinese numbers in the Eight Banners led in 1642 of all Eight Han Banners being created.