Russia had occupied the Chinese region of Manchuria in the aftermath of the 1900 Boxer Rebellion, and the United States, Japan, and Britain all sought the end of its military presence in the region. Russia agreed to withdraw its forces in 1902, but it reneged on this promise and sought to expand its influence in Manchuria to the detriment of the other powers. Roosevelt was unwilling to consider using the military to intervene in the far-flung region, but Japan prepared for war against Russia in order to remove it from Manchuria. When the Russo-Japanese War broke out in February 1904, Roosevelt sympathized with the Japanese but sought to act as a mediator in the conflict. He hoped to uphold the Open Door policy in China and prevent either country from emerging as the dominant power in East Asia. Throughout 1904, both Japan and Russia expected to win the war, but the Japanese gained a decisive advantage after capturing the Russian naval base at Port Arthur in January 1905. In mid-1905, Roosevelt persuaded the parties to meet in a peace conference in Portsmouth, New Hampshire, starting on August 5. His persistent and effective mediation led to the signing of the Treaty of Portsmouth on September 5, ending the war. For his efforts, Roosevelt was awarded the 1906 Nobel Peace Prize. The Treaty of Portsmouth resulted in the removal of Russian troops from Manchuria, and it gave Japan control of Korea and the southern half of Sakhalin Island.