Under the mediation of U.S. president Theodore Roosevelt, the Russo-Japanese War officially ended with the signing of a treaty at the Portsmouth Naval Shipyard in Maine.

Theodore Roosevelt Jr., also known as Teddy or T. R., was the 26th president of the United States, serving from 1901 to 1909. Roosevelt previously was involved in New York politics, including serving as the state's 33rd governor for two years. He served as the 25th vice president under President William McKinley for six months in 1901, assuming the presidency after McKinley's assassination. As president, Roosevelt emerged as a leader of the Republican Party and became a driving force for anti-trust and Progressive Era policies.

The Russo-Japanese War was fought between the Russian Empire and the Empire of Japan over rival imperial ambitions in Manchuria and the Korean Empire. The major land battles of the war were fought on the Liaodong Peninsula and near Mukden in Southern Manchuria, with naval battles taking place in the Yellow Sea and the Sea of Japan.

The Treaty of Portsmouth is a treaty that formally ended the 1904–1905 Russo-Japanese War. It was signed on September 5, 1905, after negotiations from August 6 to 30, at the Portsmouth Naval Shipyard in Kittery, Maine, United States. U.S. President Theodore Roosevelt was instrumental in the negotiations and won the Nobel Peace Prize for his efforts, the first ever American recipient. The treaty recognized Japan's hegemony in Korea, awarded it Russia's lease on the Liaodong Peninsula, control of the Russian-built South Manchuria Railway, and the southern half of the island of Sakhalin (Karafuto).

The Portsmouth Naval Shipyard (PNS), often called the Portsmouth Navy Yard, is a United States Navy shipyard on Seavey's Island in Kittery, Maine, bordering Portsmouth, New Hampshire. The naval yard lies along the southern boundary of Maine on the Piscataqua River.