Why did Kangxi attack the Russian fortress of Albazin?

The Kangxi emperor attacked the Russian fortress of Albazin because Russian forces had reoccupied and fortified it, along with Nerchinsk, after previously being expelled from the region.

By the mid-17th century, Russians had reached the Amur River valley. After securing his internal control over China, Kangxi turned his attention to these northern encroachments, viewing the Amur valley as part of the Manchu homeland. Following a successful attack on Albazin in 1685, the Russians returned to man the fortress once the Qing forces withdrew. This prompted Kangxi to order a second expedition and a protracted siege in 1686. These military actions were intended to assert Qing sovereignty and ultimately pressured Russia into signing the Treaty of Nerchinsk in 1689, which established the border between the two empires.1