Complex sentence: He also claimed to be a direct descendant and the reincarnation of Amursana, the Khoit-Oirat prince who led the Dzungar Khanate to destruction in 1757, and for seeking to liberate the Mongolian people from Manchu-Chinese control.
Split into simpler sentences: He also claimed to be a direct descendant and the reincarnation of Amursana, the Khoit-Oirat prince who led the Dzungar Khanate to its extermination in 1757. By so doing, Ja Lama claimed he was seeking to liberate the Mongolian people from Manchu-Chinese control.