How did Andrew caregie make most of his money?

Andrew Carnegie made most of his money through the steel industry, particularly by founding the Carnegie Steel Company in the late 19th century. He revolutionized steel production by adopting the Bessemer process, which allowed for the efficient mass production of steel. His company grew rapidly, becoming the largest and most profitable steel manufacturer in the world, contributing significantly to the expansion of America's infrastructure during the Industrial Revolution. In 1901, Carnegie sold his company to J.P. Morgan for $480 million, solidifying his status as one of the wealthiest individuals of his time.