The last decades of the 19th century were a period of imperial expansion for the United States, as it extended its influence, and at times its domain, over widely scattered areas in the Atlantic and Pacific Oceans and into Central America. The United States took a different course than its European rivals, however, because of its own history of struggle against European empires and its unique democratic development.  

The sources of American expansionism in the late 19th century were varied. Internationally, it was a period of imperialist frenzy, as European powers raced to carve up Africa and competed for influence and trade in Asia -- along with a new rival, Japan. Many Americans, including such influential figures as Theodore Roosevelt, Henry Cabot Lodge and Elihu Root, felt that to safeguard its own interests, the United States had to stake out spheres of economic influence as well. That view was seconded by a powerful naval lobby, which called for an expanded fleet and network of overseas ports as essential to the economic and political security of the nation. More generally, the doctrine of "manifest destiny," first used to justify America's continental expansion, was now revived to assert that the United States had a right and duty to extend its influence and civilization in the Western Hemisphere and the Caribbean, as well as across the Pacific.  

At the same time, the voices of anti-imperialism from diverse coalitions of Northern Democrats and reform-minded Republicans remained loud and constant. As a result, the acquisition of an American empire was piecemeal and ambivalent, and colonial administrations were often more concerned with trade and economic issues than political control.  

America's first venture beyond her continental borders was the purchase of Alaska -- sparsely populated by Inuit and other native peoples -- from Russia in 1867. Most Americans were either indifferent to or indignant at this action by Secretary of State William Seward, and Alaska was widely referred to as "Seward's Folly" and "Seward's Icebox." But 30 years later, when gold was discovered on Alaska's Klondike River, thousands of Americans headed north, and many of them settled in Alaska permanently. When Alaska became the 49th state in 1959, it replaced Texas as the largest state in the Union.  

The Spanish-American War, which was fought in 1898, marked a turning point in American history. Within a few years after the war ended, the United States was exercising control or influence over islands in the Caribbean Sea, the mid-Pacific and close to the Asian mainland.  

By the 1890s, Cuba and Puerto Rico were the only remnants of Spain's once vast empire in the New World, while the Philippine Islands comprised the core of Spanish power in the Pacific. The outbreak of war had three principal sources: popular hostility to autocratic Spanish rule; American sympathy with demands for independence; and a new spirit of national assertiveness in the United States, stimulated in part by a "jingoistic" or nationalistic and sensationalist press.  

In 1895 Cuba's growing wrath against the tyranny of the mother country burst into a war of independence. The United States watched the course of the uprising with mounting concern. Most Americans were sympathetic with the Cubans, but President Cleveland was determined to preserve neutrality. Three years later, however, during the McKinley administration, the U.S. warship Maine was destroyed while lying at anchor in Havana harbor, under circumstances that are still unclear. More than 250 men were killed, and an outburst of indignation, intensified by sensationalized press coverage, swept across the country. Although for a time McKinley tried to preserve the peace, within a few months, believing delay futile, he recommended armed intervention.  

The war with Spain was swift and decisive. During the four months it lasted, not a single American reverse of any importance occurred. A week after the declaration of war, Commodore George Dewey, then at Hong Kong, proceeded with his squadron of six vessels to the Philippines. His orders were to prevent the Spanish fleet based there from operating in American waters. He caught the entire Spanish fleet at anchor and destroyed it without losing an American life.  

Meanwhile, in Cuba, troops landed near Santiago, where, after winning a rapid series of engagements, they fired on the port. Four armored Spanish cruisers steamed out of Santiago Bay and a few hours later were reduced to ruined hulks.  

From Boston to San Francisco, whistles blew and flags waved when word came that Santiago had fallen. Newspapers dispatched correspondents to Cuba and the Philippines, who trumpeted the renown of the nation's new heroes. Chief among them were George Dewey of Manila fame and Theodore Roosevelt, who resigned as assistant secretary of the navy to lead the "Rough Riders," a volunteer regiment he recruited for service in Cuba. Spain soon sued for peace, and in the treaty signed on December 10, 1898, transferred Cuba to the United States for temporary occupation preliminary to the island's independence. In addition, Spain ceded Puerto Rico and Guam in lieu of war indemnity, and the Philippines on payment of $20 million.  

Having overseas possessions was a new experience for the United States. Consequently, the new territories were encouraged to move toward democratic self-government, a political system with which none of them had any previous experience.  

Nevertheless, the United States found itself in a familiar colonial role when it suppressed an armed independence movement in the Philippines in the first decade of its occupation. The Philippines gained the right to elect both houses of its legislature in 1916, and in 1936 a largely autonomous Philippine Commonwealth was established. In 1946, after World War II, the islands attained full independence.  

American involvement in the Pacific area was not limited to the Philippines, however. The year of the Spanish-American War also saw the beginning of a new relationship with the Hawaiian Islands. Earlier contact with Hawaii had been mainly through missionaries and casual traders. After 1865, however, Americans began to develop the islands' resources -- chiefly sugar cane and pineapples. When the royal government announced its intention to end foreign influence in 1893, American businessmen joined with influential Hawaiians to install a new government, which then asked to be annexed to the United States.  

Widespread protests in the United States against the use of American soldiers and the idea of colonial rule persuaded President Grover Cleveland and Congress to reject annexation at first. But, responding to the surge of nationalism generated by the Spanish-American War, Congress voted overwhelmingly in July 1898 to annex the islands, thus also acquiring an important naval base at Pearl Harbor. In 1959 Hawaii became the 50th state in the Union.  

Cuba acquired nominal independence when American troops departed in 1902. But the United States retained the right to intervene to preserve civil order, which it did on three occasions before renouncing that right in 1934. Even with full Cuban independence, however, American economic and political influence remained strong until 1959, when Fidel Castro overthrew the government in power, establishing a Marxist regime with close ties to the Soviet Union.  

Puerto Rico, the island lying east of Cuba, followed an apprenticeship similar to that of Cuba and the Philippines. In 1917 the U.S. Congress granted Puerto Ricans the right to elect all of their legislators. But the same law created a different path for the island, making it officially a U.S. territory and, more importantly, giving its people American citizenship. In 1950 Congress granted Puerto Rico complete freedom to decide its future. In the referendum of 1952, the citizens voted to reject either statehood or total independence, and chose instead a commonwealth status. Large numbers of Puerto Ricans have settled on the mainland, to which they have free access and where they acquire all the political and civil rights of any other citizen of the United States.