What was an unsuccessful attempt at American imperialism in the late 1800s?

When looking at American imperialism in the 1800s, we see only a few notable examples of failure. I would argue that the most notable failure of the United States came regarding the island of Cuba. In 1854, for example, Southern slaveholders in the U.S. hoped to expand slave territory. By expanding slave territory this would give them greater power in the federal government, and they hoped to utilize this power to maintain the institution of slavery. By acquiring Cuba from the government of Spain, they hoped to bring it into the Union as a new slave state.
The U.S. Secretary of State in 1854, William Marcy, sent a delegation to Belgium to negotiate with the European powers of France, Britain, and Spain regarding the acquisition of Cuba by the United States. The American delegation created a document called the Ostend Manifesto. The Ostend Manifesto explained the importance of Cuba to the United States and stated that forcefully taking Cuba may be necessary if a deal could not be reached. This attempt would ultimately fail and the United States would not realize its goal of gaining Cuba. It would also serve to complicate relations between the United States and the European powers as it reinforced their vision of the United States as an aggressive nation seeking to carve out an empire of their own.
Cuba would eventually gain independence through the Spanish-American War in 1898. After gaining independence, however, Cuba was under American supervision for decades. Although it served a supervisory role, the United States did not achieve their goal of gaining full control over Cuba.
https://www.encyclopedia.com/history/united-states-and-canada/us-history/ostend-manifesto-1854

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