Between 1858 and 1860, the Russian Empire annexed territories adjoining the Amur River belonging to the Chinese Qing dynasty through the imposition of unequal treaties. The 1858 Treaty of Aigun, signed by the general Nikolay Muravyov representing the Russian Empire and the official Yishan representing Qing China, ceded Priamurye—a territory stretching from the Amur River north to the Stanovoy Mountains, but the Qing government initially refused to recognize the treaty's validity. Two years later, the Second Opium War concluded with the Convention of Peking, which affirmed the previous treaty as well as an additional cession including the entire Pacific coast to the Korean border, as well as the island of Sakhalin to Russia. These two territories roughly correspond to modern-day Amur Oblast and Primorsky Krai, respectively. Collectively, they are often referred to as Outer Manchuria, part of the greater region of Manchuria.

The Treaty of Aigun was an 1858 treaty between the Russian Empire and Yishan, official of the Qing dynasty of China. It established much of the modern border between the Russian Far East and China by ceding much of Manchuria, now known as Northeast China. Negotiations began after China was threatened with war on a second front by Governor-General of the Far East Nikolay Muraviev when China was suppressing the Taiping Rebellion. It reversed the Treaty of Nerchinsk (1689) by transferring the land between the Stanovoy Range and the Amur River from the Qing dynasty to the Russian Empire. Russia received over 600,000 square kilometers (231,660 sq mi) of what became known as Outer Manchuria. While the Qing government initially refused to recognize the validity of the treaty, the Russian gains under the Treaty of Aigun was affirmed as part of the 1860 Sino-Russian Convention of Peking.