The annexation of Hawaii
Hawaii had been flirting with the United States since it became a whaling supply station in the early 1800s and the site of a major American missionary effort. Thanks to missionaries, Hawaii actually had the first printing press west of the Mississippi in 1822. Thanks to the king of Hawaii, John Sutter founded Sacramento (and set the stage for the gold rush) with the help of Hawaiian workers. The sons of the first missionaries planted sugar cane, and the Hawaiian government granted Pearl Harbor to the United States as a naval base.
When the McKinley Tariff made selling Hawaiian sugar in the United States more expensive, the American sugar planters in Hawaii had an easy solution. They deposed Queen Liliuokalani and asked to be admitted to the United States; Hawaii wouldn't be subject to the tariff if it were part of the United States. For five years, the United States held Hawaii off as a point of honor — it didn't want to be associated with land-grabbing. With the outbreak of the Spanish-American War, the United States got over national worries about honor and annexed Hawaii.
The Spanish-American War
Sugar also made problems in Cuba when high U.S. import duties caused fewer sales and more hardship for the sugar workers. The workers rose in revolt against the Spanish colonial government, which suppressed them violently.
The United States was sympathetic to the workers' plight, and yellow journalists egged the country on toward war with Spain. Sensationalist newspaperman William Randolph Hearst sent famous Western artist Frederick Remington to Cuba to draw pictures of the atrocities. When Remington cabled that conditions weren't bad enough for a war, Hearst cabled back, "Please remain. You furnish the pictures and I'll furnish the war."
Losing the battleship Maine
At the worst possible time for the Spanish, the U.S. battleship Maine, which had been sent to Cuba on a "goodwill" visit, blew up in Havana harbor. Four independent investigations over the past 100 years have come to four different conclusions about what caused the explosion, but at the time everybody but the Spanish believed that Spain had torched it. Congress voted to invade Cuba, but also passed the Teller Amendment (1898), which promised to free Cuba after the island was free of the Spanish.
Using some tricky fighting, the United States first attacked the Spanish not in Cuba but in Spain's Philippine Islands colony, halfway around the world. The U.S. fleet sailed into Manila harbor, pulverized the Spanish fleet, and then sat around sweltering through the tropical summer, waiting for American troops to get there and take the islands. With the help of Filipino insurrectionists, the American army made short work of the Spanish troops.
Cuba was the same story. The American navy smashed the Spanish without losing a ship, and the American army, with Teddy Roosevelt leading the Rough Riders, quickly defeated the Spanish troops. The army still had a few Civil War veterans from 33 years before; Northerners and Southerners felt good about fighting on the same side.
Letting Cuba go but keeping the rest
To end the one-sided Spanish-American War, Spain agreed to give the United States control of Cuba, the Philippines, and Puerto Rico. The United States, feeling a little guilty, generously kicked in $20 million for the Philippines, because they were kind of a bonus for freeing Cuba. Puerto Rico came as a free bonus, which America decided to keep.
U.S. expansionism at the end of the 1800s is a natural stopping place for any essay discussion on Manifest Destiny you may have to undertake on the AP U.S. History exam. Remember: Imperialism is keeping colonies; expansionism is adding land that becomes a real part of the mother country. With the Philippines free, Hawaii a state, and Puerto Rico regularly voting to stay with the United States, the end of the United States's 1890s overseas adventures came out as expansionism.
The United States set Cuba free as promised, keeping only a naval base at Guantanamo Bay, which was a little bigger than Manhattan. Having successfully invaded once, the United States felt free to intervene in Cuba any time it wanted to — until Fidel Castro took power in 1958.
Fighting in the Philippines
The Philippines were trickier. European countries, especially Germany, were still sniffing around the world for colonies. The United States decided to keep the Philippines for a few years to establish a government and build some schools and roads. That meant fighting a bloody war against the same Filipino revolutionaries who had just finished helping America get rid of the Spanish.
The Philippines conflict lasted for five years and led to the deaths of thousands of soldiers on both sides and hundreds of thousands of civilians caught in the crossfire. The United States finally freed the Philippines in 1946, after World War II.
Rejecting the idea of empire
The U.S. flirtation with empire, especially keeping the Philippines, was opposed by a lot of Americans, including Mark Twain, Andrew Carnegie, former President Grover Cleveland, Jane Addams, and the presidents of Harvard and Stanford universities.
Eventually, the imperialist eagle came to rest with the release of Cuba and the Philippines; Puerto Rico and Hawaii were mostly agreed about staying part of the United States. As the United States increasingly became a world power, the temptation to push smaller nations around never went away.
Question: What was the biggest controversy following the Spanish-American War?
Answer: Americans debated whether freedom-loving America had any right to keep the Philippine Islands as a colony.