In the first years of the 20th century the people of Phoenix recognized that the region’s potential was limited by its unreliable water supply. They formed the Salt River Valley Water Users’ Association to lobby for the creation of a large-scale project to control the flow of the river and harness its water for irrigation. The National Reclamation Act of 1902 had made government funding available for such public works. In 1905 construction began on the Roosevelt Dam, the first such structure on the Salt River; it was finished in 1911, making it possible to irrigate the surrounding desert and thus use it as farmland. In following years three more dams were added on the Salt and two on the Verde River.

With a network of reservoirs in place, Phoenix grew as an important agricultural centre in the early 20th century, providing winter vegetables and grain for much of the West. During World War I many of the city’s farms shifted to the production of Egyptian (pima) cotton, which was needed for use in clothing, tires, airplane fabrics, and munitions. Russian, Japanese, and Mexican migrant workers traveled to Phoenix to work in the cotton fields, and by the 1920s the city underwent a cotton boom. A decade later the Great Depression put an end to such prosperity. Facing that unexpected downturn in the agricultural economy, Phoenix’s business community—led by Dwight Heard, John Orme, William Murphy, and other prominent citizens—worked to diversify the city’s economy, especially by encouraging the development of tourism.

During World War II Arizona’s deserts served as military bases. Many of the soldiers who passed through Arizona liked what they saw and returned at the end of the war. Several hundred German and Italian prisoners of war who had been interned in camps in and near Phoenix chose to remain rather than return to their homelands after 1945.

Postwar growth

The population grew substantially in the decade following the war, as affordable home air-conditioning became available. During that time hundreds of manufacturing firms relocated from other parts of the country. By 1960 half of the state’s population lived in the Phoenix area.

Another factor in Phoenix’s growth was the arrival of another source of water. Arizona Senators Carl Hayden and Barry Goldwater lobbied for a massive public works project, and in 1968 the Colorado River Basin Project Act was passed. The act authorized the CAP, which involved constructing a series of dams along with a canal that would divert water from the Colorado River to be used by many communities, including Phoenix and Tucson.

The military presence in the Phoenix area also contributed to the city’s rapid growth. Until the 1930s, Camp McDowell was the sole military outpost in the region; in the years preceding World War II, however, Phoenix’s business elite, led by Goodyear Tire chairman Frank Littlefield, successfully lobbied for the relocation of several U.S. Army Air Corps detachments to the area. Two important air bases, Williams and Luke, were established, and the military brought in thousands of personnel, many of whom remained or returned after completion of their service. In the aftermath of the Cold War, the military presence was reduced somewhat, but the U.S. Air Force has continued to figure prominently in the local economy and be an important employer of civilians.

Corruption and conflict

In the late 1960s and early ’70s corruption was an impediment to convincing nonmilitary employers to move into the Phoenix area. Bruce Babbitt, who in the mid-1970s was the state attorney general, warned that not only the Phoenix area but the entire state had earned reputations beyond their borders as dens of vice and crime. Land fraud was common, as was the illegal use of undocumented workers—mostly from Mexico and Central America—in factories and farms at extremely low pay rates. In 1976 Arizona Republic reporter Don Bolles was murdered while investigating the connections between organized crime and agriculture and banking within Arizona; public outcry brought on several criminal conspiracy trials and the imprisonment of such crime figures as Ned Warren, locally known as the “Godfather of land fraud.” The spectre of corruption emerged again in the late 1980s, when Phoenix financier and developer Charles Keating was convicted on the charge of having stolen more than $1 billion from a financial firm that he controlled. The institution’s demise was one of the largest bank failures in the country’s history.

Into the 21st century

With increased prosperity in the 1990s, many of the city’s social ills, notably crime, lessened, and material conditions improved. In 1993 the CAP, construction of which began in the early 1970s, was officially completed. The city continued to grow through policies of annexation and promotion to bring businesses to the area. By the early 21st century Phoenix and the once-distinct cities that surround it had emerged as one of the largest metropolitan areas in the country in terms of both area and population.