The expansion of wheat agriculture in the Great Plains created several problems. In 1930s, terrifying dust storms began to blow over the southern plains. As the skies darkened, and the dust swept in, people were blinded and choked. Cattle were suffocated to death. Tractors and machines that had ploughed the earth and harvested the wheat in the 1920s were now clogged with dust, damaged beyond repair. In part they came because the early 1930s were years of persistent drought. The rains failed year after year, and temperatures soared. But ordinary dust storms became black blizzards only because the entire landscape had been ploughed over, stripped of all grass that held it together. Zealous farmers had recklessly uprooted all vegetation, and tractors had turned the soil over, and broken the sod into dust. The whole region had become a dust bowl. The American dream of a land of plenty had turned into a nightmare. The settlers had thought that they could conquer the entire landscape, turn all land over to growing crops that could yield profits. After 193, they realized that they had to respect the ecological conditions of each region.