外東北
The Treaty of Nerchinsk signed in 1689 after a series of conflicts, defined the Sino–Russian border as the Stanovoy Mountains and the Argun River, making Outer Manchuria a part of Qing China. After losing the Opium Wars, Qing China was forced to sign a series of treaties that gave away territories and ports to the imperialist Western powers as well as to Russia and Japan; these were known as the Unequal Treaties. Starting with the Treaty of Aigun in 1858 and the Treaty of Peking in 1860, the Sino–Russian border was realigned in Russia's favor along the Amur and Ussuri rivers. As a result, China lost Outer Manchuria (an area of more than 1 million km2) and access to the Sea of Japan.