In 1900, world politics centered on the capitals of Europe: Berlin, London, Paris, St. Petersburg, and Vienna. European empires, led by the British and the French, controlled vast stretches of territory across all the continents and seas. By the end of the 20th century, Europe's position in world affairs had changed totally. There are a number of reasons: the decline of the empires; the expanding power of the United States; the development of independent nation states across the world; the emergence of China as a world power; and the new economic strength of Asia.