The Russo-Japanese War was a conflict between the Russian Empire and the Empire of Japan from 1904 to 1905. The major cause of the war was the dispute over control of Manchuria and Korea. Russia had long sought to expand its influence in East Asia, while Japan had sought to become the dominant power in the region. The war ended with a Japanese victory, resulting in the Treaty of Portsmouth, which granted Japan control of Korea and the southern half of Sakhalin Island.