What hesitations and doubts about imperialism did Americans evince between 1865 and 1898? How did the Spanish-American War change all this?

Though initially opposed to imperialism, the U. S.’s economy was overproducing due to industrialization where there surpluses to their products. Apart from that, they were searching for other sources of raw materials that they needed for production. Another reason for the change was that some thought that by entering into imperialism, they were continuing America’s vision of Manifest Destiny. The Spanish-American War gave them that opportunity where they acquired Guam, the Philippines and Puerto Rico from the Spaniards.