U.S. President Theodore Roosevelt tests a steam shovel during construction of the Panama Canal in 1906.

"Is America a weakling, to shrink from the work of the great world powers? No!" then-Navy Secretary Theodore Roosevelt noted in an 1897 letter. "The young giant of the West stands on a continent and clasps the crest of an ocean in either hand."

To that end, the United States went to war against Spain in 1898, a conflict that supporters proclaimed would liberate Cuba from colonial oppression. Once the Spanish were vanquished, however, President William McKinley's administration quickly moved to make sure that the liberators, not the liberated, had real control. The U.S. Army barred Cuban rebels from entering Santiago (the capital at the time), and put officials from the deposed Spanish administration back in control of the city. The United States soon established a military government to rule the island.

As U.S. troops suppressed labor strikes in Havana, American companies bought up land, minerals and timber rights — what historian Philip Foner called the "commercial occupation" of Cuba. The Cubans eventually were allowed to set up their own government in 1901, but only after they agreed to accept the Platt Amendment, which gave the United States the legal right to intervene in Cuba whenever it deemed necessary.

When McKinley's successor, Theodore Roosevelt, wanted to build an Atlantic-Pacific canal across the isthmus of Panama, which was then part of Columbia, he resorted to an even more cynical version of nation-building. In 1903, American agents fomented a Panamanian rebellion against the Columbian government, and U.S. gunships moved in to block the Columbians from stopping it. Roosevelt then hastily recognized the new Panamanian regime, which in turn agreed to accept $10 million and an annual $250,000 fee in exchange for the canal site.

The United States also intervened in another Central American nation, Nicaragua, in part to prevent the building of a rival canal. In the 1910s and 1920s, U.S. Marines were stationed there to prevent political parties deemed unfriendly to U.S. interests from gaining power. U.S. troops finally pulled out in 1933, leaving behind a military controlled by a pro-U.S. general, Antonio Somoza Garcia, who eventually became dictator.