Prior to 1914, a good team of horses or mules provided all the power the typical Midwestern farmer needed. If his tillable land exceeded 100 acres, he may have had more than one team. At harvest, when belt power was needed to drive a threshing machine, the farmer hired a steam engine. Horses pulled wagons loaded with bundles to the threshing site and hauled the separated wheat, barley or oats to the storage bins. After 1915, though, two unrelated events contributed to a rapid change from horses and mules to tractors: the introduction of the automobile, and the scarcity of food in Europe resulting from the upheaval caused by World War I.