Treaty of Aigun
During the Xianfeng Emperor's reign, China lost part of Manchuria to the Russian Empire. In 1858, according to the Treaty of Aigun, the territory between Stanovoy Mountains and Amur River was ceded to Russia, and in 1860, according to the Treaty of Beijing, the same thing happened also to the area east of Ussuri River. After that treaty, the Russians founded the city of Vladivostok in the area they had annexed.