After the Spanish–American War in 1898 the United States strengthened its power in the Caribbean by annexing Puerto Rico, declaring Cuba a virtual protectorate in the Platt Amendment (1901), and manipulating Colombia into granting independence to Panama (1904), which in turn invited the United States to build.
In the years after World War II, the United States was guided generally by containment — the policy of keeping communism from spreading beyond the countries already under its influence. The policy applied to a world divided by the Cold War, a struggle between the United States and the Soviet Union.