Prior to America's expansion into the rest of the world, it was quite focused on domestic issues. However, with the Civil War being long over, and postwar politics settled, America was ready for expansion into foreign soil. There were several justifications for imperialism. However, they were mainly triggered towards the economic success of the United States. Also, several events helped speed up the process of acquiring the territory. Yet, although Alfred T. Mahan, religion, and Darwinism all called for imperialism, the United States was mainly driven by possible economical gains as seen in the acquisition of Cuba, Hawaii, and Puerto Rico as well as with the Insular Cases and Platt Amendments that flaunted American power.
Hawaii had long been populated by White Americans prior to its annexation in 1898. Yet, when the McKinley Tariff was imposed, Americans were forced to pay a tax on Hawaiian sugar. Thus, harming planter profits. This tariff had the planters calling for annexation. Although, Queen Liliuokalani tried to block their ambition, she was eventually taken out of power before the United States took over completely.
Around the same time as the struggle for Hawaii, Americans claimed to be sympathizing with Cubans and their suffering in reconcentration camps. With the aid of the yellow press, America was able to furnish a war to fight for Cuban liberty. The Teller Amendment, which promised Cuba freedom upon victory over Spain, helped the American public believe the war was being fought strictly to help the poor Cubans. Yet, it is easy to see that having a foothold on our conveniently nearby neighbor Cuba would tremendously aid the American navy.
Upon the end of the Spanish-American war, the United States also gained control over the Philippines as well as Puerto Rico for a bargain of 20 million dollars. Aside from personal desires, the United States had no reason, other than economical gains for taking over this territory. The citizens of these territories saw no real benefit from the United States taking over.
The Insular Cases serve as evidence that the new American territories acquired nothing from being taken over by Americans. The Insular Cases denied these people rights that American citizens enjoyed. In other words, they established that the constitution does not follow the flag. The United States expanded in order to expand its economical power. Although they claimed to have fought the Spanish-American war in order to free the Cubans, the Platt Amendment basically made Cuba an American puppet. With this amendment, Americans had control over Cuba, and gave themselves the power to use Cuban territory for naval stations.
The dawn of imperialism was justified by religion and Darwinism. However, the continuation of it was driven by the desire for economical gains. Indeed, the United States profited from these territorial gains. Eventually, imperialism helped establish the United States as a world power.