The pivotal moment that marked the shift from an agrarian economy to an industrialized society in the U.S. was the Industrial Revolution, particularly in the late 19th century. Innovations in technology, transportation, and production methods significantly altered economic practices, leading to increased urbanization and the growth of factories. This transformation allowed for mass production, changing labor dynamics and contributing to economic growth. The Industrial Revolution laid the foundation for modern economic structures, social classes, and the expansion of the U.S. as an industrial power.