Europe is one of the seven continents of Earth, taking up 3,930,000 square miles (2% of Earth and 6.8% of its land area). The continent is the world's second-smallest continent after Oceania, and Russia takes up 39% of the continent, also having the largest population. Europe has a popualtion of 752,452,000, 11% of the world population, with its native inhabitants being Caucasians. Europe was the birthplace of Western civilization, seeing the civilizations of Ancient Greece and Ancient Rome, the Classical Era, the Middle Ages, the Renaissance, Enlightenment, the Industrial Revolution, the world wars, the Cold War, and the modern era. Today, much of the continent is united under the European Union, which has a common currency (the Euro), citizenship, and borders.