Final answer:
After building his bridge, Andrew Carnegie continued to innovate and dominate the steel industry, practicing vertical integration and becoming a major philanthropist in his later life.
Step-by-step explanation:
Andrew Carnegie, after building his successful steel bridge, continued to expand and solidify his position in the steel industry.
Carnegie implemented strategies such as vertical integration, taking control over every aspect of steel production to lower costs by owning mines, foundries, and railroads. His investments and management of the steel industry dramatically transformed the United States infrastructure, leading to innovative production methods and resulting in his company's massive profits. Carnegie's success culminated in the sale of his enterprise to J.P. Morgan in 1901 for an outrageously inflated sum of $500 million, which led to the creation of the U.S. Steel Corporation, the country's first billion-dollar firm. Later in life, Carnegie became a significant philanthropist, donating much of his wealth to various charitable causes including libraries, schools, and institutions of higher education.