In the middle of the eighteenth century, the Qing empire’s invasion of what is now Xinjiang resulted in the destruction of Zünghar Mongol society and their almost complete extermination as a people. The policy of mass killing represented the failure of the first Qing military campaigns into the steppe to incorporate the fragmenting Zünghar polity. Continuing violence, exacerbated by famine and disease, drove the Qianlong emperor to issue instructions to exterminate the ‘mahachin’, i.e. Zünghar Mongols who had sought refuge from the invasion and/or were still holding out. This chapter charts the historical background to this conflict, situates it in a wider Inner Asian context, and offers a close analysis of the events and imperial decrees that triggered the descent into indiscriminate killing. Despite the ferocity of the campaign, the Zünghars were not entirely wiped out, and I conclude by discussing the resettlement of survivors and their fate during the remainder of the Qing Dynasty.