The Battle of Liège was the opening engagement of the German invasion of Belgium, and the first battle of World War I. The attack on the city began on 5 August 1914[2] and lasted until the 16th when the last Belgian fort finally surrendered. The invasion of Belgium was the event that triggered the United Kingdom's entry into the war; the unexpected vigor of the city's defence allowed more time for the western Allies to organize and prepare their defence of France.