Answer:
With the conquest of land in the west, the oppression of the Indians, the forcible appropriation of Texas and other areas of Mexico in 1848, the American policy, influenced by its own sense of mission, the Manifest Destiny, showed imperialist features early on. Before the Civil War, the internal American debate about the admission of slavery had led to considerable delays in the discussion of one's own position on colonies when it expanded to the American continent. This imperialist view was defended by many, but mostly by conservatives, called "war eagles".
With the victory in the Spanish-American War in 1898, the United States also entered the circle of imperialist world powers. The acquisition of the Philippines and Puerto Rico as well as the occupation of Cuba and the construction of the Panama Canal were also seen in the domestic political debate as the first step towards competing with the European colonial powers.
After its victory in World War I, the United States received German island groups in the Pacific from the League of Nations as mandate areas. During the Second World War, other Pacific islands came under US rule.
The foreign policy of the USA in South and Central America up to the 1980s, with its interventions and influences, is often cited as an example of neo-imperial power politics.
