What major inovation of the late 19th century transformed the business of retailing in the US?

The major innovation of the late 19th century that transformed the business of retailing in the U.S. was the establishment of department stores. These large retail establishments combined a wide variety of goods under one roof, offering consumers a one-stop shopping experience. They introduced modern marketing techniques and customer service practices, such as fixed pricing and return policies, which made shopping more accessible and enjoyable for the general public. Additionally, the rise of mail-order catalogs further expanded retail access, allowing consumers in rural areas to purchase goods conveniently.