Manstein Plan in the context of "Battle of Sedan (1940)"

Army Group A (German: Heeresgruppe A) was the name of three distinct army groups of the Heer, the ground forces of the Wehrmacht, during World War II.

The first Army Group A, previously known as "Army Group South", was active from October 1939 to June 1941 and notably served in the Battle of France as the decisive army group in the implementation of the "Sickle Cut" military plan that inflicted crushing subsequent defeats on the French armed forces at occasions such as the Battle of Sedan, Battle of Boulogne and Battle of Dunkirk and that ultimately led to the Armistice of 22 June 1940. Army Group A was subsequently used in the German occupation of France and temporarily became the first Oberbefehlshaber West in German-occupied France. It was eventually replaced in this function by Army Group D and redeployed to German-occupied Poland in preparation for Operation Barbarossa. At the commencement of that attack, Army Group A was renamed "Army Group South" on 22 June 1941, ending the first deployment.

The invasion of Belgium or Belgian campaign (10–28 May 1940), often referred to within Belgium as the 18 Days' Campaign (French: Campagne des 18 jours; Dutch: Achttiendaagse Veldtocht), formed part of the larger Battle of France, an offensive campaign by Germany during the Second World War. It took place over 18 days in May 1940 and ended with the German occupation of Belgium following the surrender of the Belgian Army.

On 10 May 1940, Germany invaded Luxembourg, the Netherlands, and Belgium under the operational plan Fall Gelb (Case Yellow). The Allied armies attempted to halt the German Army in Belgium, believing it to be the main German thrust. After the French had fully committed the best of the Allied armies to Belgium between 10 and 12 May, the Germans enacted the second phase of their operation, a break-through, or sickle cut, through the Ardennes, and advanced toward the English Channel. The German Army (Heer) reached the Channel after five days, encircling the Allied armies. The Germans gradually reduced the pocket of Allied forces, forcing them back to the sea. The Belgian Army surrendered on 28 May 1940, ending the battle.

The Battle of Dunkirk (french: Bataille de Dunkerque) was fought around the French port of Dunkirk (Dunkerque) during the Second World War, between the Allies and Nazi Germany. As the Allies were losing the Battle of France on the Western Front, the Battle of Dunkirk was the defence and evacuation of British and other Allied forces to Britain from 26 May to 4 June 1940.

After the Phoney War, the Battle of France began in earnest on 10 May 1940. To the east, the German Army Group B invaded the Netherlands and advanced westward. In response, the Supreme Allied Commander, French General Maurice Gamelin, initiated "Plan D" and British and French troops entered Belgium to engage the Germans in the Netherlands. French planning for war relied on the Maginot Line fortifications along the German–French border protecting the region of Lorraine but the line did not cover the Belgian border. German forces had already crossed most of the Netherlands before the French forces had arrived. Gamelin instead committed the forces under his command – three mechanized forces, the French First and Seventh Armies and the British Expeditionary Force (BEF) – to the River Dyle. On 14 May, German Army Group A burst through the Ardennes and advanced rapidly westward toward Sedan, turning northward to the English Channel, using Generalfeldmarschall Erich von Manstein's plan Sichelschnitt (under the German strategy Fall Gelb), effectively flanking the Allied forces.