The Liáodōng Peninsula is a peninsula in the Liáoníng province of northeastern China, historically known in the west as southern east-Manchuria. Liaodong (formerly spelled Liaotung) means "East of the Liáo". The Liáo River was a river during the Warring States that divided the Yan commandries of Liáoxī (west of the Liáo) and Liaodong.
The two seaports, Dalian which lies midway along the peninsula at its narrowest point and Port Arthur/Lushun (now a consolidation of several municipalities known as Lüshun City), which is located at its southernmost point. Lüshun City is the governmental district seat of the 2 southernmost "Dalian districts" (county-level government), known as Lüshunkou (literally "Lüshun Port"), organized under the sub-provincial city of Dalian. Lüshun/Port Arthur has a large lake-like naturally-protected harbor and semi-sheltered outer roadstead making it very attractive to imperialist powers at the end of the nineteenth century. Dalny/Dairen/Dalian's harbor required greater investment, initially supplied by the Russians, but turned into a first class city under the Japanese period of administration (1905–1945). The two ports are about apart by rail, but about apart by sea. Lüshun is 550 rail miles south of the Manchurian railroad hub city of Harbin on the historic Southern Manchurian Railway (today's China Far East Railway (CER), which construction was one of the underlying causes of the Russo-Japanese War).
The peninsula was an important area of conflict during the First Sino-Japanese War (1894–1895), which the Japanese won. Defeat precipitated decline in the Chinese Empire which was exploited by colonial powers who extracted numerous concessions. The peninsula was ceded to Japan by the Treaty of Shimonoseki of April 17, 1895 but this was rescinded after the Triple Intervention of April 23, 1895 by Russia, France and Germany. In the aftermath of this intervention, the Russian government pressured the ruling Qing dynasty to lease Liaodong and the strategically important Lüshunkou (Port Arthur) for use by the Russian Navy. This caused resentment in Japan and was a factor leading to the Russo-Japanese War (1904–1905) when negotiations concerning the peninsula, Manchuria, and Korea broke down, due to Russia's unwillingness to treat seriously with Japan as another power. As in the First Sino-Japanese War the Liaodong peninsula was the scene of major fighting in the Russo-Japanese War. As a consequence of the Treaty of Portsmouth (September 5, 1905), which ended the Russo-Japanese War, both sides agreed to evacuate Manchuria and return its sovereignty to China, but Japan was given the lease for the Liaotung/Liaodong.