Final answer:
Andrew Carnegie was the man most responsible for the development of the steel industry in America. He financed the creation of a modern steel mill and controlled every aspect of the steel-making process, allowing him to produce better steel for lower prices than his competitors.
Step-by-step explanation:
The man most responsible for the development of the steel industry in America was Andrew Carnegie.
Carnegie, a Scottish immigrant, rose through the ranks of corporate America to create a domestic steel industry based on new technologies he had observed in Britain.
He financed the creation of a modern steel mill and controlled every aspect of the steel-making process, allowing him to produce better steel for lower prices than his competitors. Carnegie's US Steel corporation eventually produced more steel than the entire British Empire.