Between 1800 and 1930, most of this natural environment was destroyed. Settlers transformed what they called "the Great American Desert" or "The Inland Sea" into farmland. They replaced the old grasses with new ones, mostly wheat and maize. They replaced the bison with cattle, another kind of bovine. About 40% of the world's maize grows in the United States, mostly on land that formerly grew grass. The grazing pattern of European cattle, the near-extermination of prairie dogs, and the plowing and cultivation of the land did the damage. Plowing cut tallgrass root systems and interrupted reproduction. Drainage changed the soil's water content, and soil erosion lost soil.