Manchuria is a term that refers to a region in Northeast Asia encompassing the entirety of present-day Northeast China, and historically parts of the modern-day Russian Far East, often referred to as Outer Manchuria. Its definition may refer to varying geographical extents as follows: the Chinese provinces of Heilongjiang, Jilin, and Liaoning but broadly also including the eastern Inner Mongolian prefectures of Hulunbuir, Hinggan, Tongliao, and Chifeng, collectively known as Northeast China; the aforementioned regions plus the homelands of ancient Jurchen and their descendant Manchus, parts of these region were ceded to the Russian Empire by the Manchu-led Qing dynasty during the Amur Annexation of 1858–1860, which include present-day Amur Oblast, Primorsky Krai, the Jewish Autonomous Oblast, the southern part of Khabarovsk Krai, and the eastern edge of Zabaykalsky Krai, collectively known as the Outer Manchuria or Russian Manchuria.

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.