Direct answer: The United States proposed the Open Door Policy to safeguard American economic interests in China by ensuring equal access to Chinese markets for all foreign powers and to prevent any single nation from carving China into exclusive spheres of influence that would exclude the United States from trade. Context and key points:

• Economic motive: American businesses sought access to the vast Chinese market and feared being shut out as other powers had already secured concessions and spheres of influence in China. The policy aimed to level the playing field so U.S. merchants could compete in China alongside European rivals.

• Preventing monopolies: By advocating an Open Door, the United States argued that no single nation should monopolize trade with China, thereby limiting the ability of powers like Britain, Germany, or Japan to exclude others from Chinese markets.

• Maintaining Chinese sovereignty: The policy was framed as preserving China's territorial and administrative integrity by avoiding formal partition or outright colonial division of China, while pursuing commercial access for all nations.

• Diplomatic context: Secretary of State John Hay articulated the policy in notes sent to major powers in 1899–1900, seeking broad assent to equal economic opportunities in China, not special privileges for any power. The policy relied on informal understanding rather than binding treaties, and its effectiveness varied in practice.

If you’d like, I can provide a brief timeline of the Open Door policy’s key statements and their reception by different countries, or compare it to related policies and events (e.g., Boxer Rebellion, later Taft and Roosevelt foreign policies).