The Treaty of Portsmouth, signed in 1905, concluded the Russo-Japanese War. Negotiated under the mediation of U.S. President Theodore Roosevelt, the treaty recognized Japan's paramount interest in Korea and ceded the southern half of Sakhalin Island to Japan. The treaty marked a significant shift in power dynamics, as it was the first time an Asian nation defeated a European power in modern history, demonstrating Japan's emergence as a major world power. It also set the stage for future international relations in the region and influenced Japanese expansionist policies.