One often overlooked chapter of the Second World War is the German invasion of Belgium. While the Battle of France is often studied, the Battle of Belgium which came before it was still vital to the course of the war. It saw the Belgian army along with British and French forces attempt to hold back the German armies. Their attempts were in vain, though, and Brussels would fall on May 17th and the nation surrendered on the 28th.
The Battle of Belgium began in earnest on May 10th with the execution of Fall Gelb, Case Yellow. In accordance with this plan the Netherlands, Luxembourg, and Belgium all were invaded with the intent of drawing Allied armies into the Low Countries. The Germans were successful in this effort, as a large portion of the British and French armies entered Belgium thinking the attack there was the main one, as it had been in the last war. Between the 10th and the 12th of May the Germans launched their invasion through the Ardennes Forest, cutting off the Allied forces in the Low Countries. Despite this, the Belgian army continued to fight, manning successive defensive lines and maintaining its cohesion even as German forces advanced with air superiority. Allied forces, in particular French tanks, were able to inflict heavy casualties on German armored units but the Germans reportedly outmaneuvered Allied troops and undid any tactical victories. Repeated Allied counterattacks were thrown back and the Germans occupied the City of Brussels on May 17th. The British and French at this time understood that the Belgians would not be able to hold, but, with the agreement of the Belgian King, tasked them with protecting the British Expeditionary Force while it attempted to retreat. On May 21st the Germans advanced to the English Channel and fully cut the Allies off. The British withdrew to Dunkirk on May 26th and two days later the Belgians surrendered. By that time, most of Belgium had been occupied, the Germans controlled the air, and what little of Belgium was left was congested with civilian refugees. The Belgian King did not set up a government in exile, but one was set up by civilian officials.
The Battle of Belgium was perhaps more crucial to the Fall of France than the actual Battle of France was. The isolation and destruction of the best elements of the British and French armies left France woefully unprepared for a German offensive, and by the time the Germans invaded France itself the outcome was essentially a foregone conclusion. Belgium would remain under German occupation until 1944 when it was liberated by American and British forces.