South Manchuria Railway in the context of "Convention for the Lease of the Liaotung Peninsula"

The colonial expansion of the Empire of Japan in the Western Pacific Ocean and East Asia began in 1895 with Japan's victory over the Chinese Qing dynasty in the First Sino-Japanese War. Subsequent victories over the Russian Empire (Russo-Japanese War of 1904-1905) and the German Empire (World War I) expanded Japanese rule. Taiwan came under Japanese control from 1895, Korea in 1905, Micronesia in 1914, Southern Sakhalin in 1905, several concessions in China from 1903 onwards, and the South Manchuria Railway from 1905. In 1931, Japan invaded Manchuria, resulting in the establishment of the puppet state of Manchukuo the following year; thereafter, Japan adopted a policy of founding and supporting puppet states in conquered regions. These conquered territories became the basis for what became known as the Greater East Asia Co-Prosperity Sphere from 1940. (The Co-Prosperity Sphere expanded to include much of China, Indo-China, Malaya, the Philippines, the East Indies, Burma and New Guinea by 1942.)

Including Mainland Japan, colonies, occupied territories, and puppet states, the Empire of Japan at its apex was one of the largest empires in history. The total amount of land under Japanese sovereignty reached 8,510,000 km (3,300,000 sq mi) in 1942. By 1943, it accounted for more than 20% of the world's population at the time, with 463 million people in its occupied regions and territories.

The Mukden incident was a false flag event staged by Japanese military personnel as a pretext for the 1931 Japanese invasion of Manchuria.

On September 18, 1931, Lieutenant Suemori Kawamoto of the Independent Garrison Unit [ja] of the 29th Japanese Infantry Regiment [ja] detonated a small quantity of dynamite close to a railway line owned by Japan's South Manchuria Railway near Mukden (now Shenyang). The explosion was so weak that it failed to destroy the track, and a train passed over it minutes later. The Imperial Japanese Army accused Chinese dissidents of the act and responded with a full invasion that led to the occupation of Manchuria, in which Japan established its puppet state of Manchukuo five months later.

The South Manchuria Railway Zone (Japanese: 南満州鉄道附属地, romanized: Minami Manshū Tetsudō Fuzoku-chi; simplified Chinese: 南满洲铁道附属地; traditional Chinese: 南滿洲鐵道附屬地; pinyin: Nán Mǎnzhōu Tiědào Fùshǔ-dì; Wade–Giles: Nan Man-chou Tʻieh-tao Fu-shu-ti) or SMR Zone, was the area of Japanese extraterritorial rights in northeast China, in connection with the operation of the South Manchurian Railway.

The Treaty of Portsmouth is a treaty that formally ended the 1904–1905 Russo-Japanese War. It was signed on September 5, 1905, after negotiations from August 6 to 30, at the Portsmouth Naval Shipyard in Kittery, Maine, United States. U.S. President Theodore Roosevelt was instrumental in the negotiations and won the Nobel Peace Prize for his efforts, the first ever American recipient. The treaty recognized Japan's hegemony in Korea (which soon after became a protectorate of the Empire of Japan), awarded it Russia's lease on the Liaodong Peninsula (which became the Kwantung Leased Territory), control of the Russian-built South Manchuria Railway, and the southern half of the island of Sakhalin (Karafuto).

The Manchukuo National Railway (Traditional Chinese and Japanese kanji: 滿洲國有鐵道, Japanese romanization: Manshū Kokuyū Tetsudō) was the state-owned national railway company of Manchukuo. Generally called the "國線" ("National Line", Kokusen), it was controlled by the Manchukuo Ministry of Transportation and had its lines primarily in the central and northern parts of the country. In local newspapers it was simply referred to as "國鉄" (Japanese: Kokutetsu, "National Rail"). It was built, operated and managed by the South Manchuria Railway, a state-owned national railway company of the Empire of Japan, of which the Kwantung Army frequently intervened in its affairs.