A decade before the American Revolution, Glasgow instrument maker James Watt was assigned with repairing a Newcomen steam engine. He quickly realized the design could be improved by adding an external condenser coil, which greatly increased thermal efficiency. The Watt steam engine soon saw widespread use in mining, textile, and other industries. Mills and factories sprung up, workers moved to the cities, and the world’s agrarian society was gradually transformed into one of mechanization. The First Industrial Revolution had begun.

Industrial growth was soon stymied, however, by a shortage of inexpensive steel. Once again, a simple invention—the introduction of compressed air into a furnace filled with molten pig iron—changed everything. English inventor Sir Henry Bessemer patented his new process in 1856, and began using it to produce steel far more quickly and at a fraction the cost of competing methods. The growing use of electricity and Henry Ford’s development of assembly line production methods during the early 1900s further bolstered this second phase of the industrial revolution, paving the way for our modern industrial society.