High Quality Content by WIKIPEDIA articles! 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 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 defense allowed more time for the western Allies to organize and prepare their defense of France.