Final answer:
Andrew Carnegie used horizontal integration to dominate the American steel industry.
Step-by-step explanation:
Andrew Carnegie used the technique of horizontal integration to dominate the American steel industry. Horizontal integration is a strategy where a company acquires or merges with competing companies in the same industry to gain control and increase market share. Carnegie's company, Carnegie Steel Company, bought out or merged with numerous steel companies, controlling the entire steel production process from mining to distribution.
Learn more about Andrew Carnegie's use of horizontal integration in the American steel industry