Germany's strategy for a war on two fronts against France and Russia was to rapidly concentrate the bulk of its army in the West to defeat France within 6 weeks, then shift forces to the East before Russia could fully mobilise; this was later known as the Schlieffen Plan. On 2August, Germany demanded free passage through Belgium, an essential element in achieving a quick victory over France. When this was refused, German forces invaded Belgium on 3August and declared war on France the same day; the Belgian government invoked the 1839 Treaty of London and, in compliance with its obligations under this treaty, Britain declared war on Germany on 4August. On 12 August, Britain and France also declared war on Austria-Hungary; on 23August, Japan sided with Britain, seizing German possessions in China and the Pacific. In November 1914, the Ottoman Empire entered the war on the side of Austria-Hungary and Germany, opening fronts in the Caucasus, Mesopotamia, and the Sinai Peninsula. The war was fought in (and drew upon) each power's colonial empire also, spreading the conflict to Africa and across the globe.