Short answers, pulled from the story.
The Dzungar Khanate was the last nomadic empire of Oirat Mongol origin, existing from roughly 1634 to 1758. At its greatest extent it covered an area from southern Siberia in the north to Tibet in the south, and from western Mongolia to present-day Kazakhstan.
Erdeni Batur, son of Kharkhul, established the Dzungar Khanate on the upper Emil River south of the Tarbagatai Mountains after being granted the title of Khong Tayiji. He built Ghulja as the capital city, invaded the Kazakh Khanate beginning in 1635, and created formal diplomatic ties with the Tsardom of Russia. His rule ended with his death in 1653.
The Dzungar Khanate collapsed due to internal succession disputes after the death of Galdan Tseren in 1745, which the Qianlong Emperor exploited by sending an army of 50,000 in 1755. The Qing conquered Dzungaria between 1755 and 1758 and, according to historian Peter Perdue, launched an explicit policy of extermination that destroyed 70-80 percent of the Dzungar population.
The Qing scholar Wei Yuan recorded that the Dzungar population before the conquest was around 600,000 in 200,000 households. Wen-Djang Chu concluded that 80 percent of the 600,000 or more Dzungars were destroyed by disease and attack. Roughly 40 percent of households were killed by smallpox, 20 percent fled to Russia or Kazakh tribes, and 30 percent were killed by Manchu bannermen.
Historian Mark Levene described the extermination of the Dzungars as arguably the eighteenth century genocide par excellence. Peter Perdue has argued it resulted from an explicit extermination policy by the Qianlong Emperor, who repeatedly used the term jiao (extermination) in orders and punished commanders who failed to carry out killings with sufficient thoroughness.
After the destruction of the Dzungar people, the Qing dynasty sponsored the settlement of millions of Han, Hui, Xibe, Uyghur, and Manchu people in the depopulated land. Scholar Stanley W. Toops has noted that modern Xinjiang's demographic situation still reflects that Qing settlement policy. Cities including Ürümqi and Yining were in effect created by it.