In American history, the "Giled Age" refers to major 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, from 1877 to 1900. The wealth polarization derived from industrial and population expansion. The entrepreneurs 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 the rising super-rich industrialists and financiers such as Cornelius Vanderbilt, John D. Rockefeller, Andrew Carnegie, Henry Flagler, and J.P. Morgan. Their critics called them "robber barons", referring to their use of overpowering and sometimes unethical financial manipulations. There was a small, growing labor union movement, led in part by Samuel Gompers, who created the American Federation of Labor (AFL).