"This was the era in which the accumulated wealth of America's richest families—the Rockefellers, the Vanderbilts, the Carnegies—helped prompt creation of the modern income tax, lest disparities in wealth turn the United States into a European-style aristocracy."

http://www.slate.com/articles/news_and_politics/the_great_divergence/features/2010/the_united_states_of_inequality/introducing_the_great_divergence.html