Second World War.
On May 10, 1940, Nazi Germany invaded Belgium, as well as Luxembourg, and The Netherlands during the Blitzkrieg offensive, which involved bombardment followed by a fast surprise attack by mobile forces. Belgium capitulated after 18 days. France and Britain sent troops into Belgium but French troops surrendered and British troops retreated from the continent via Dunkirk, in France. The Belgian government fled to France, then to London. King Leopold III, as commander in chief of the army, remained in Belgium and was confined to his palace by the Germans, who remained there until Allied forces reached Belgium on September 3, 1944. The Belgian underground army prevented the destruction of the port of Antwerp. Belgium was the location of the Ardennes Offensive, also known as the Battle of the Bulge, a surprise attack by the German army on December 16, 1944, seeking to split the British and American Allied line in half, capturing Antwerp, Belgium, and then proceeding to encircle and destroy four Allied armies, forcing the Western Allies to negotiate a peace treaty. The German objectives ultimately were unrealized. In the wake of the defeat, many experienced German units were left severely depleted of men and equipment, as German survivors retreated to the defenses of the Siegfried Line. Belgium lost 86,100 people to that war.