Almost 600 miles from north to south, Great Britain is the ninth-largest and third-most-populated island in the world, with about 66 million inhabitants. Despite its relatively small area, it contains immense scenic variety. Although much of southern England is crowded and heavily urbanized, most of northern Scotland is a wilderness of lakes and mountains, populated chiefly by red deer. During the most recent ice age, Britain was part of continental Europe and only became an island again when the glaciers retreated and sea levels rose, around 6500 B.C. Today the Channel, separating England from France, is 21 miles wide at its narrowest point. The three nations of England, Wales and Scotland are politically united but still intensely protective of their individual identities.