Miami's growth up to World War II was astronomical. In 1900, 1,681 people lived in Miami, Florida; in 1910, there were 5,471 people; and in 1920, there were 29,549 people. As thousands of people moved to the area in the early 1900s, the need for more land quickly became apparent. Up until then, the Florida Everglades only extended to three miles west of Biscayne Bay. Beginning in 1906, canals were made to remove some of the water from those lands. Miami Beach was developed in 1913 when a two-mile wooden bridge built by John Collins was completed. During the early 1920s, the authorities of Miami allowed gambling and were very lax in regulating Prohibition, so thousands of people migrated from the northern United States to the Miami region. This caused the first Florida construction boom and many high-rise buildings were built: some early developments were razed after their initial construction to construct larger buildings. The population of Miami doubled from 1920 to 1923. The nearby areas of Lemon City, Coconut Grove and Allapattah were annexed in the fall of 1925, creating the Greater Miami area.

This speculation boom started to falter because of building construction delays. The transport system was contantly overloaded with bulky building materials. In January of 1926 the Prinz Valdemar, an old Danish warship on its way to becoming a floating hotel, ran aground and blocked Miami Harbor for weeks. Already overloaded, the three major railway companies soon declared an embargo on all incoming goods except food. The cost of living had skyrocketed and finding an affordable place to live was nearly impossible. This economic bubble was already collapsing when the catastrophic Great Miami Hurricane in 1926 ended what was left of the boom. According to the Red Cross, there were 373 fatalities. Other estimates vary, since there were a large number of people listed as "missing". Between 25,000 and 50,000 people were left homeless in the Miami area. The Category 4 storm was the 12th most costly and 12th most deadly to strike the United States during the 20th century. The Great Depression followed, in which more than sixteen thousand people in Miami became unemployed. A Civilian Conservation Corps camp was opened in the area.

In the mid-1930s, the Art Deco district of Miami Beach was developed. On February 15, 1933, an assassination attempt was made on President-elect Franklin D. Roosevelt by Giuseppe Zangara, an Italian anarchist, while Roosevelt was giving a speech in Miami's Bayfront Park. Mayor Anton Cermak of Chicago, who was shaking hands with Roosevelt, was shot and died two weeks later. Four other people were wounded, but President-elect Roosevelt was not harmed. At his sentencing Zangara said, "I decide to kill him and make him suffer. I want to make it 50-50. Since my stomach hurt I want to make even with capitalists by kill the President. My stomach hurt long time." Zangara was quickly tried for Cermak's murder and was executed by the electric chair on March 20, 1933 in Raiford, Florida.

Miami Beach