Answer :
It was the Spanish-American War, which took place in 1898 led to the changes in the size of the United States.
• In 1898, the Spanish-American War terminated the colonial empire of Spain in the Western Hemisphere and the position of the United States as a Pacific power got secured.
• In the war, the victory of United States generated a peace treaty that compelled the Spanish to cede sovereignty over Puerto Rico, Guam, and the Philippines to the United States, and to relinquish claims on Cuba.
• During the war, the independent state of Hawaii also go annexed by the United States.
Thus, the war allowed the United States to establish its dominance in the Caribbean region and to pursue its economic and strategic interest in Asia. Therefore, the Spanish-American War in 1898 led to changes in the size of the United States.
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