What amendment turned Cuba into a protectorate of the United States?

The Platt Amendment is the correct choice because it explicitly set the terms under which the United States would withdraw its military from Cuba following the Spanish-American War, while also outlining the conditions for Cuba's relations with other nations. Ratified in 1901, this amendment effectively established Cuba as a U.S. protectorate, allowing for U.S. intervention in Cuban affairs to preserve its independence and maintain order. Additionally, it restricted Cuba's ability to enter into treaties with other nations and required Cuba to lease land for U.S. naval bases, further solidifying American influence over the island.

By contrast, the Teller Amendment, passed in 1898 in the context of the war with Spain, declared that the U.S. aimed to liberate Cuba and would not annex the island. The Boxer Protocol, established in 1901, pertains to China and does not relate to U.S.-Cuban relations. The Hawaii Annexation Act, which was related to the annexation of Hawaii in 1898, also does not pertain to Cuba or its status as a protectorate. Each of these other options represents a different context or event and does not address the specific relationship established between the United States and Cuba as defined by the Platt Amendment.