On the same day that hostile soldiers marched into Belgium, the German emperor, Kaiser Wilhelm, proclaimed war with the French. And with the Germans now setting foot on Belgian territory, the Belgians called upon the terms of the Treaty of London. This was an agreement that had been signed by the European powers in 1839.
This treaty, among other things, assured the neutrality of Belgium. The Germans had clearly flouted the terms of the 75-year-old agreement and the British government felt they had no option but to declare war on Germany. This was despite the fact that Wilhelm was the cousin of the British King George V. In fact, another cousin to both of them was Russia’s Tsar Nicholas II.