Final answer:
U.S. businesses in the mid 19th century enjoyed minimal government intervention, adhering to laissez-faire economics, with businesses like Carnegie Steel and Standard Oil dominating the market. Increased regulation came in the early 20th century to address monopolies and protect consumers and workers.
Step-by-step explanation:
The behavior of U.S. businesses under the free enterprise system in the mid 19th century is best characterized by minimal government intervention. During this period, businesses operated with substantial freedom from government constraints, a concept known as laissez-faire economics. This period was marked by the dominance of companies like the Carnegie Steel Company and the Standard Oil Company, which epitomized the social darwinism business practices of the era. They were able to grow by cutting costs, optimizing profits, offering low wages, and controlling their markets without significant interference from government regulation.
However, by the early 20th century, the growing power of monopolies led reformists and the government to recognize the need for more regulation to ensure fair competition and to protect consumers and workers.