With each advance in transportation technology, cities have spread out. Horses increased the useful distances in towns; horse-drawn buses of the early 1800s widened that distance. Electric trolleys enlarged cities further, and commuter steam trains enabled the growth of suburbs. Elevators allowed cities to expand upward.

New forms of transport tended, at the outset, to be somewhat expensive, so it was the wealthy who first used them, often to get to new homes farther from downtown’s noise and crowds. As the automobile became a main mode of transport, highway systems formed that connected the country but also made it easy to commute to work from well outside the city. New towns cropped up around driving, and older cities began losing population. The result was urban centers surrounded by wide suburban sprawls.

Following the Second World War, the US established mortgage loan guarantees and tax deductions to help servicemen afford a house. William Levitt, a returning Navy Seabee construction officer, bought up 20 square miles of land on Long Island, and, inspired by Henry Ford’s assembly-line system, mass-produced and sold thousands of small, inexpensive, good-quality homes complete with appliances. Levitt cut costs by avoiding both unions and middlemen; his houses, ridiculed by architecture critics, proved wildly popular.