Final answer:
The McCormick reaper revolutionized the economy of the Northwest region prior to the Civil War, enabling states like Ohio, Indiana, and Illinois to greatly increase wheat production and become major agricultural states.
Step-by-step explanation:
The invention of the McCormick reaper revolutionized the economy of the Northwest region prior to the Civil War. Thanks to the mechanization provided by the McCormick reaper, farmers in states like Ohio, Indiana, and Illinois were able to vastly increase their output of wheat, transforming agriculture in the area north of the Ohio River into the pantry for the major cities in the East. As a result, these states became major agricultural states, with reduced food prices and improved efficiency in grain harvest, fostering the rapid development of the upper Midwest as a dominant agricultural region known as "King Wheat".
The McCormick Harvesting Machine Company helped popularize this revolutionary farming machine by establishing operations in Chicago, where labor was more available. The reaper allowed for faster harvesting than the traditional scythe, and in partnership with advancements made by John Deere in plow design, it helped open the prairies to more extensive agriculture, supporting greater yields and contributing to the region's economic growth.