By the time the United States entered the twentieth century, it had acquired Hawaii, the Philippines, Puerto Rico, and Guam. Theodore Roosevelt, who became president in 1901, started the building of the Panama Canal. He also established the United States as a police officer among Latin American nations.
From April 1917 to November 1918, the United States helped its European allies fight and win World War I. After the war, the United States became recognized as a leader among the world's most powerful nations.
Americans experienced a booming economy during the 1920s. Near the end of the 1920s, however, the Great Depression replaced the good life. During the 1930s, President Franklin D. Roosevelt tried to fight the Depression with his New Deal programs. Laws passed during the New Deal introduced into legislation the belief that the federal government has a duty to help Americans in need.
From 1941 to 1945, Americans joined World War II to help stop the Axis powers from overrunning Europe and the Pacific. After the war, the United States and the Soviet Union, a Communist country, emerged as the world's superpowers. Differences between the two superpowers and their allies created the cold war. Trying to stop the spread of the communism, the United States took part in open warfare in Korea (1950-1953) and Vietnam (1965-1973). During the cold war era, Americans also started the civil rights movement, attacked poverty, and witnessed the first resignation of a president.
