John Hay was the U.S. Secretary of State who implemented the Open Door policy in China in 1899-1900 to promote American trading interests in the region. The U.S. wanted a closer connection with China after acquiring nearby territories in Guam, the Philippines, and Hawaii and after realizing that China was a good market for American goods, including cotton textiles. The Open Door policy became the cornerstone of American foreign policy in China for the next 40 years. Other countries, including Britain, Russian, France, Germany, and Japan tried to protect their trading interests and spheres of influence in China, but the U.S., which had no sphere of influence and little power in the region, was interested in promoting free trade in China. As part of the policy, Hay advocated that Chinese tariffs be applied equally in each region and that the Chinese government collect taxes. He wanted to implement this policy to ensure that the tax money went to the Chinese, not to other powers, and so that the Chinese would not favor one foreign power over another. 

Other countries, save Russia, agreed to the American trade terms (though they weren't binding). However, the Boxer Rebellion, which broke out in China in 1900, threatened the terms of the Open Door Policy. As martial arts experts began to attack foreign missionaries and Christian converts during the Boxer Rebellion, foreign troops started to carve special interests as they made their way to the Chinese capital to save their countrymen. In 1900, Hay again asked the other powers to respect the terms of the Open Door Policy, though the terms of the agreement weren't binding. The Open Door Policy ushered in a period of intense U.S. involvement in China that ended in 1949 with the communist takeover of China.