From the mid-1800s until the mid-1900s, American toy makers used cast iron to make toys for the growing number of middle-class families. Manufacturers preferred cast iron because the United States had rich deposits of iron ore, coal, and limestone-three crucial materials in the production of usable iron-and because the sand-mold process streamlined production and reduced costs. Cast-iron vehicles became especially popular, including horse-drawn fire wagons, circus wagons, trains, cars, planes, and streetcars. Cast-iron toys remained in production until World War II, when manufacturers dedicated their time and materials to the war effort.