The Mechanical Reaper:
Before McCormick's reaper, grain was harvested by hand and the short harvesting season limited farm size and food availability. When the reaper was released, it was an instant success, and even won first place at the World's fair of 1851 in London.
Not only did McCormick's reaper increase harvest production, but it also helped the development of the Midwest. In the late 1840s, McCormick decided to move his company to Chicago, which was still an up and coming city. He did this based on a theory that the midwestern states such as Illinois, Indiana, Wisconsin, and the soon to be territories of Kansas and Nebraska were the future of American agriculture. His bet ended up turning out very well for him.