Russo-Japanese War

The Russo-Japanese War was fought from February 1904 to September 1905 between the Russian Empire and the Empire of Japan. Its underlying cause was the collision of two expansionist projects in Northeast Asia: Russia's southward push into Manchuria following its lease of the Liaodong Peninsula and Port Arthur (1898), and Japan's drive to consolidate a sphere of influence over Korea after its victory in the First Sino-Japanese War (1894–1895). Diplomatic negotiations in 1903 failed to produce a mutually acceptable demarcation between Russian interests in Manchuria and Japanese interests in Korea.

Japan opened hostilities with a surprise naval attack on the Russian Pacific Squadron at Port Arthur on the night of 8–9 February 1904. Major land engagements followed at the Yalu River, Liaoyang, and Mukden, the last (February–March 1905) being one of the largest land battles fought up to that date. At sea, Admiral Tōgō Heihachirō's Combined Fleet destroyed the Russian Baltic Fleet — which had sailed around the world to reach the theatre — at the Battle of Tsushima on 27–28 May 1905.

The war was ended by the Treaty of Portsmouth, signed on 5 September 1905 in New Hampshire and mediated by U.S. President Theodore Roosevelt, who later received the 1906 Nobel Peace Prize for his role. Russia recognised Japan's paramount interests in Korea, transferred its Liaodong leasehold and the South Manchurian Railway to Japan, and ceded the southern half of Sakhalin.

The conflict is widely treated in IR scholarship as a turning point: it was the first modern war in which an Asian power decisively defeated a European great power, accelerated the 1905 Russian Revolution, fed Japanese militarism culminating in the 1910 annexation of Korea, and previewed the industrial-scale trench warfare and naval gunnery of World War I.