During the Gilded Age, there was substantial growth in population in the United States and extravagant displays of wealth and excess of America's upper-class during the post-Civil War and post-Reconstruction era, in the late 19th century. The wealth polarization derived primarily from industrial and population expansion. The businessmen of the Second Industrial Revolution created industrial towns and cities in the Northeast with new factories, and contributed to the creation of an ethnically diverse industrial working class which produced the wealth owned by rising super-rich industrialists and financiers called the "robber barons". An example is the company of John D. Rockefeller, who was an important figure in shaping the new oil industry. Using highly effective tactics and aggressive practices, later widely criticized, Standard Oil absorbed or destroyed most of its competition.