Answer:
The Open Door Policy intended to protect the right of all countries to trade equally with China. It "was a major statement of United States foreign policy issued in 1899 and 1900 [...] confirming multi-national acknowledgment of China’s administrative and territorial sovereignty. Proposed by U.S. Secretary of State John Hay and supported by President William McKinley, the Open Door Policy formed the foundation of U.S. foreign policy in East Asia for more than 40 years."
Reference: Longley, Robert. “What Was the Open Door Policy in China? Definition and Impact.” ThoughtCo, ThoughtCo, 29 Aug. 2019