German Kaiser Wilhelm II and British King George V discussing operation orders, 1913. Today 109 years ago, on August 4, 1914, the United Kingdom declared war on Germany following the German invasion of Belgium on the same day. At 8:02 AM on August 4, 1914, the first German troops began crossing the Belgian border on their way to France, thereby breaching Belgian neutrality. In 1839, the the United Kingdom had ratified and signed the Treaty of London, serving to recognise and guarantee the independence and neutrality of Belgium in case of invasion. The German invasion on August 4, 1914 was a plain breach of this treaty, which Britain would use as their gateway to declare war on Germany and enter the First World War. At 2 PM on August 4, British Foreign Secretary Sir Edward Grey sent a British ultimatum to Germany by telegraph demanding that Germany respect the neutrality of Belgium and pull out her troops, with a German reply required before 11 PM. By 10:45 PM, no German response had be...