Andrew Carnegie, the 19th century Pittsburgh industrialist, was one of the richest Americans ever, and also a benevolent civic patron. Nasaw, a self-described "lunatic researcher," wrote a biography simply titled "Andrew Carnegie." Early in December he shared what he learned at the Minnesota Historical Society's History Forum in St. Paul.Carnegie is credited with leading the steel industry expansion in the United States, persuading manufacturing companies to switch from iron to steel, which was more expensive but more durable. Carnegie operated the companies that built new infrastructure as well as the companies that provided the supplies, Nasaw said, and "that's why Mark Twain calls this a gilded age of corruption." In 1900, Carnegie sold his steel manufacturing company to turn to philanthropy full time, announcing he would give away all of his wealth. "And he gives it away in huge quantities," Nasaw said. "Now the question is, why?" Some historians say it was because he felt guilty for contributing to the harsh working conditions for steel workers."And then I read his prenuptial," Nasaw said. Written long before working conditions deteriorated at Carnegie's steel plants, the prenuptial agreement stated that his wife, Louise Whitfield Carnegie, would get an allowance” but would receive nothing when he died, because he had already decided to give it away."Why did he do it? Because Andrew Carnegie above everything else was a thinker, a social philosopher, an observer of the world around him, and it was his self-assigned task in life to figure out what it meant," Nasaw said. "It" being the great deal of wealth he had accumulated in his life. Carnegie concluded it was because he was best suited to give it back to the workers, in the form of things he thought they needed” like building a library instead of raising their pay” something he openly admitted to during a speech at the Carnegie Library of Pittsburgh.