What policy did the US implement in relation to China in 1900?

The correct answer, the Open Door Policy, was a significant diplomatic stance introduced by the United States in 1900 concerning trade with China. This policy aimed to ensure equal trading rights for all foreign nations in China and to prevent any one nation from monopolizing Chinese trade. The underlying belief was that allowing multiple countries access to Chinese markets would help foster international cooperation and maintain China's territorial integrity.

The Open Door Policy emerged in the context of various powers attempting to expand their influence over China, especially after the Boxer Rebellion in 1900, which was an anti-foreign uprising. With this policy, the United States sought to protect its commercial interests in China while promoting fair competition and giving China the chance to manage its own internal affairs without being subjected to the control of any single foreign nation.

In contrast, the other options refer to different historical contexts. The Yellow Peril Policy relates to the fear and prejudice against Asian immigrants in the United States, while the Monroe Doctrine was a principle that opposed European colonialism in the Americas. The Good Neighbor Policy was an approach focused on improving relations with Latin American countries in the 20th century.