Gerdan is the leader of Zhungeer Department in West Mongolia, and once became a monk in Tibet. Later, when his brother died, he returned to northern Xinjiang, won the political struggle, succeeded Zhungeer Khan and became the leader of Zhungeer Department.
After that, through continuous expansion, most tribes in western Mongolia were initially unified and became the overlord of Mongolian grassland. Then it continued to expand eastward, gradually threatening the Mongolian ministries that had been conquered before the Qing Dynasty entered the customs.
For the Qing dynasty, Mongolia in the west can be ignored, but the Mongolian tribes in the middle and east must be stable. Because this part of Mongolia is regarded by the rulers of Qing Dynasty as a part closer to itself than the Han people, and it is more trustworthy than the Han people.
Therefore, the Qing Dynasty can accept a unified Mongolian regime in the west, but it can't allow others to take away the sovereignty of the eastern and central Mongolian tribes from themselves.
So first of all, Grdan's power expanded eastward, threatening the Qing Dynasty's rule over the tribes in central and eastern Mongolia. The Qing dynasty thought that it had threatened its own foundation and must fight back.
Secondly, during the Kangxi period, Gedan took the initiative to attack the Qing Dynasty, not the Qing Dynasty. In other words, Kangxi fought passively for the first time, not actively provoked war.
Gerdan attacked the Qing Dynasty with two intentions. One is to determine their sovereignty over Mongolia by defeating the Qing army, to become the only supreme ruler of Mongolian ministries, and to seize Mongolian ministries from the Qing Dynasty.
On the other hand, I hope to establish a tributary relationship with the Qing Dynasty similar to that of the early Han Dynasty through a large-scale active attack on the Qing Dynasty, so as to obtain some materials from the mainland under the rule of the Qing Dynasty and establish its own trade hegemony.
However, Grdan's first attack was not successful, but was defeated by the Qing army and forced to return to the grassland. The Qing army took the initiative for the second time, hoping to return Mongolia to the control of the Qing dynasty and defeat the main force of Gerdan. However, the initiative of the Qing army failed to achieve the expected results.