The Treaty of Portsmouth was an agreement signed in 1905 that ended the Russo-Japanese War, a conflict between Russia and Japan over territorial disputes in East Asia. The treaty was negotiated in Portsmouth, New Hampshire, with the help of U.S. President Theodore Roosevelt, who played a crucial role in bringing both sides to the negotiating table. Under the terms of the treaty, Russia recognized Japan's control over Korea and ceded parts of Manchuria to Japan. This marked Japan's emergence as a major world power and shifted the balance of power in East Asia, leading to increased tensions in the region in the years that followed.