Russo-Japanese War  -  1904-1905 conflict between Imperial Russia and Japan primarily over Manchuria. The Japanese routed and embarrassed the Russians and defeated their fleet. At the Battle of Mukden, which the Japanese won, more soldiers (624,000) were involved than in any battle before or since. The Treaty of Portsmouth, mediated by US President Teddy Roosevelt, ended the war, and gave Japan a protectorate in nominally-independent Korea.