Final answer:
John Hay sent the Open Door notes to ensure U.S. commercial interests were protected in China by proposing equal trading rights for all nations, preventing the colonization of China, and maintaining open access to Chinese markets for American goods.
Step-by-step explanation:
John Hay sent the Open Door notes to the European powers and Japan to counter the threat of China being divided among those powers and to ensure that the United States maintained access to China's lucrative markets. By proposing that all nations should have their trading rights and privileges respected within China, Hay sought to protect American commercial interests and prevent the colonization and partition of China that would lock out U.S. traders. The Open Door notes outlined a policy where China would trade with all countries on equal terms, maintaining China’s territorial integrity while allowing American goods to compete fairly in the vast Chinese market.