"A century's worth of technology, legislation, and plain old capitalism made our homes what they are today," Dan Cray writes in This Old House magazine. According to Cray, the 15 milestones that changed housing include guaranteed mortgage loans, indoor plumbing, refrigeration, and the development of synthetic fibers. For a quick look at changes in North American house styles over the centuries, be sure to explore our photo encyclopedia of Favorite House Styles.