In the North, urbanization and an unprecedented influx of immigrants from Southern and Eastern Europe supplied a surplus of labor for the country's industrialization and transformed its culture. National infrastructure including telegraph and transcontinental railroads spurred economic growth and greater settlement and development of the American Old West. The later invention of electric light and the telephone would also affect communication and urban life.

United States and its territories at their greatest extent from 1898 to 1902

The end of the Indian Wars further expanded acreage under mechanical cultivation, increasing surpluses for international markets.Mainland expansion was completed by the purchase of Alaska from Russia in 1867.In 1893, pro-American elements in Hawaii overthrew the monarchy and formed the Republic of Hawaii, which the U.S. annexed in 1898. Puerto Rico, Guam, and the Philippines were ceded by Spain in the same year, following the Spanish–American War.

Rapid economic development during the late 19th and early 20th centuries fostered the rise of many prominent industrialists. Tycoons like Cornelius Vanderbilt, John D. Rockefeller, and Andrew Carnegie led the nation's progress in railroad, petroleum, and steel industries. Banking became a major part of the economy, with J. P. Morgan playing a notable role. Edison and Tesla undertook the widespread distribution of electricity to industry, homes, and for street lighting. Henry Ford revolutionized the automotive industry. The American economy boomed, becoming the world's largest, and the United States achieved great power status. These dramatic changes were accompanied by social unrest and the rise of populist, socialist, and anarchistmovements.This period eventually ended with the advent of the Progressive Era, which saw significant reforms in many societal areas, including women's suffrage, alcohol prohibition, regulation of consumer goods, greater antitrust measures to ensure competition and attention to worker conditions.