In a crucial turning point of the Russo-Japanese War, Japan captures Port Arthur, a major Russian naval base on the Liaodong Peninsula in China, on this day in 1905.

When Czar Nicholas II’s Russia declined to withdraw its troops from Manchuria after joining with British, French, Japanese, German and American forces to suppress the Boxer Rebellion in China in 1900, Japan became wary of Russia’s territorial ambitions in the Far East. On February 4, 1904, the Japanese launched a surprise attack on Port Arthur, beginning the Russo-Japanese War.

Port Arthur, which was called Lushun by the Chinese, had been an important port in the area as far back as the 6th century. Occupied in 1858 by the British, it was later used by the Chinese as a naval base to guard the entrance to Bao Hai, or the Gulf of Chihli, in the 1880s. Japan attacked and briefly held the city in 1895, but beginning in 1898 it had been leased to the Russians, who heavily fortified the naval base and renamed the city Port Arthur.

In light of the defeat at Port Arthur in January 1905, as well as the bitter and violent rebellion he faced within his own country, Czar Nicholas accepted the offer of U.S. President Theodore Roosevelt to broker a peace between Russia and Japan. Under the terms of the Treaty of Portsmouth—signed in Portsmouth, New Hampshire, in August 1905—control of Port Arthur and the surrounding region was transferred to the Japanese, who renamed the city Ryojun. Ryojun would serve as an important naval base and the seat of government in the territory as well the main port for Japanese-controlled Manchuria until the end of World War II, when the area was placed under joint Soviet-Chinese control. Full Chinese sovereignty in Lushun was restored in 1955.

The surprising triumph in 1905 of upstart Japan over formidable Russia upset the traditional balance of power in Europe, exposing Russia’s growing vulnerability and foreshadowing the even greater upheaval that was to come.