In 1871, the Treaty of Frankfurt ratified the loss of Alsace-Moselle by France. It benefited the new German Empire, proclaimed a few months earlier, in the Hall of Mirrors of the Palace of Versailles. The region remained attached to it until the end of World War I. The 1,597,000 Alsatians and inhabitants of Moselle were then considered Germans. They could, however, opt for French nationality before October 1st, 1872, provided they left the territory. Nearly 9% of the population thus emigrated mainly to Nancy, in Lorraine, and Belfort. The Château du Haut-Koenigsbourg became a symbol of German integration.