Western Europe is the western region of Europe. The region's extent varies depending on context. The concept of "the West" appeared in Europe in juxtaposition to "the East" and originally applied to the Western half of the ancient Mediterranean world, the Latin West of the Roman Empire, and "Western Christendom". Beginning with the Renaissance and the Age of Discovery, roughly from the 15th century, the concept of Europe as "the West" slowly became distinguished from and eventually replaced the dominant use of "Christendom" as the preferred endonym within the area. By the Age of Enlightenment and the Industrial Revolution, the concepts of "Eastern Europe" and "Western Europe" were more regularly used. The distinctiveness of Western Europe became most apparent during the Cold War, when Europe was divided for 40 years by the Iron Curtain into the Western Bloc and Eastern Bloc, each characterised by distinct political and economical systems.