If the steam engine mobilized industry, the automobile mobilized people. While ideas for personal vehicles had been around for years, Karl Benz's 1885 Motorwagen, powered by an internal combustion engine of his own design, is widely considered the first automobile. Henry Ford's improvements in the production process -- and effective marketing -- brought the price and the desire for owning an auto into the reach of most Americans. Europe soon followed.
The automobile's effect on commerce, society and culture is hard to overestimate. Most of us can jump in our car and go wherever we want whenever we want, effectively expanding the size of any community to the distance we're willing to drive to shop or visit friends. Our cities are largely designed and built around automobile access, with paved roads and parking lots taking up huge amounts of space and a big chunk of our governments' budgets. The auto industry has fueled enormous economic growth worldwide, but it's also generated a lot of pollution.