Amur River in the context of "Outer Manchuria"

Northeast China (Chinese: 东北; pinyin: Dōngběi) is a geographical region of China, consisting officially of three provinces Liaoning, Jilin and Heilongjiang. The heartland of the region is the Northeast China Plain, the largest plain in China with an area of over 350,000 km (140,000 sq mi). The region is separated from the Russian Far East to the north and east by the Amur, Argun and Ussuri Rivers; from North Korea to the south by the Yalu and Tumen Rivers; and from the neighboring North China to the west by the Greater Khingan Range and Yan Mountains. It is also bounded by the Bohai Bay and Yellow Sea to the southwest, about 100 km (62 mi) away from East China's Jiaodong Peninsula across the Bohai Strait, due to be connected via a proposed undersea tunnel.

The four prefectures of Inner Mongolia (which is part of North China) east of the Greater Khingan, i.e. Chifeng, Tongliao, Hinggan and Hulunbuir, are sometimes also considered broader parts of Northeast China, and together with the aforementioned three provinces formed what was historically known as Inner Manchuria, in contrast to the Outer Manchuria (or "Outer Northeast" in Chinese literatures) annexed by the Russian Empire during the mid-19th century.

Khabarovsk Krai (Russian: Хабаровский край, romanized: Khabarovskiy kray, IPA: [xɐˈbarəfskʲɪj kraj]) is a federal subject (a krai) of Russia. It is located in the Russian Far East and is administratively part of the Far Eastern Federal District. The administrative centre of the krai is the city of Khabarovsk, which is home to roughly half of the krai's population and the largest city in the Russian Far East (just ahead of Vladivostok). Khabarovsk Krai is the third-largest federal subject by area, and had a population of 1,343,869 as of 2010.

Being dominated by the Siberian High winter cold, the continental climates of the krai see extreme freezing for an area adjacent to the sea near the mid-latitudes, but also warm summers in the interior. The southern region lies mostly in the basin of the lower Amur River, with the mouth of the river located at Nikolaevsk-on-Amur draining into the Strait of Tartary, which separates Khabarovsk Krai from the island of Sakhalin. The north occupies a vast mountainous area along the coastline of the Sea of Okhotsk, a marginal sea of the Pacific Ocean. Khabarovsk Krai is bordered by Magadan Oblast to the north; Amur Oblast, Jewish Autonomous Oblast, and the Sakha Republic to the west; Primorsky Krai to the south; and Sakhalin Oblast to the east.

The Nivkh, or Gilyak (also Nivkhs or Nivkhi, or Gilyaks; ethnonym: Нивхгу, Nʼivxgu (Amur) or Ниғвңгун, Nʼiɣvŋgun (E. Sakhalin) "the people"), are an indigenous ethnic group inhabiting the northern half of Sakhalin Island and the lower Amur River and coast on the adjacent Russian mainland. Historically, they may have inhabited parts of Manchuria.

Nivkh were traditionally fishermen, hunters, and dog breeders. They were semi-nomadic, living near the coasts in the summer and wintering inland along streams and rivers to catch salmon. The land the Nivkh inhabit is characterized as taiga forest with cold snow-laden winters and mild summers with sparse tree cover. The Nivkh are believed to be the original inhabitants of the region, and to derive from a proposed Neolithic people that migrated from the Transbaikal region during the Late Pleistocene.

Aigun (simplified Chinese: 瑷珲; traditional Chinese: 璦琿; pinyin: Ài Hún; Manchu: ᠠᡳ᠌ᡥᡡᠨ aihūn; Russian: Айгунь, romanized: Aigun) was a historic Chinese town in northern Manchuria, situated on the right bank of the Amur River, some 30 kilometres (19 mi) south (downstream) from the central urban area of Heihe (which is across the Amur from the mouth of the Zeya River and Blagoveschensk).

The Chinese name of the town, which literally means "Bright Jade", was a transliteration of the Manchu (or Ducher) name of the town. The current Mainland Chinese pronunciation Ài Huī does not reflect this, unlike the Taiwanese pronunciation which still follows the Old National Pronunciation Ài Hún.

Khabarovsk (Russian: Хабаровск [xɐˈbarəfsk] ) is the largest city and the administrative centre of Khabarovsk Krai, Russia, located 30 kilometers (19 mi) from the China–Russia border, at the confluence of the Amur and Ussuri Rivers, about 800 kilometers (500 mi) north of Vladivostok. As of the 2021 Russian census, it had a population of 617,441. It was known as Khabarovka until 1893.

The city was the administrative center of the Far Eastern Federal District of Russia from 2002 until December 2018, when the status was given to Vladivostok. As is typical of the interior of the Russian Far East, Khabarovsk has an extreme climate with strong seasonal swings resulting in strong, cold winters and relatively hot and humid summers.

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 Heishui Mohe (Chinese: 黑水靺鞨; pinyin: Hēishuǐ Mòhé; Manchu: Sahaliyan i Aiman or 薩哈廉部; Korean: 흑수말갈; RR: Heuksu malgal), rendered in English as Blackriver Mohe or Blackwater Mohe, were a tribe of Mohe people in Outer Manchuria along the Amur River (Chinese: 黑水; pinyin: Hēi Shuǐ; lit. 'Blackwater" or "Black River') in what is now Russia's Khabarovsk Krai, Amur Oblast, Jewish Autonomous Oblast, and Heilongjiang in China.