On the afternoon of August 3rd, 1914, Germany declared war on France, two days after it had declared war on Russia. France responded by also declaring war, against Germany. Archduke Franz Ferdinand and his wife had been assassinated by nineteen year-old Gavrilo Princip in support of Serbian nationalism in Sarajevo seven weeks previously, sparking unrest in the Balkans.
On August 3, 1914, German troops were positioned on the frontier of Belgium, which was neutral, as on August 2nd the country and its king had been given a German ultimatum. Because Belgium’s neutrality had been mandated by a treaty between the European powers,including Britain, France and Germany, Sir Edward Grey, the British Foreign secretary had convinced Parliament to support to Britain going to war if Belgian neutrality was violated on August 2nd.