It was considered a turning point, because at the time the U.S. was in the American-Spanish war. It took place from April to August in 1898. the war ended in victory for the United States and the end of the Spanish Empire in the Pacific and Caribbean. Only ~113 days after the outbreak of war, the Treaty of Paris, which ended the conflict, gave the United States control over the former Spanish colonies of Puerto Rico, the Philippines and Guam, and control over the process of independence of Cuba, which was completed in 1902.
