Let me explain.  Everyone knows that the 19th Century, its uprightness, its optimism and sense of purpose, the halcyon days of British Empire, came to an end with World War I, starting in 1914 and building to a nasty crescendo by 1916.  The 20th Century had arrived, and it had some real horrors in store for us.
 

But if we return back another hundred years, we notice that the 18th Century ends in 1815 with the final defeat of Napoleon, that final project of the Enlightenment and of the French Revolution.  With the Congress of Vienna in 1814-1815, we have a new Europe along the lines of Metternich's plan, and the 19th Century at last is here.