The Battle of France, also known as the Fall of France, was the German invasion of France and the Low Countries in 1940 during the Second World War. In six weeks from 10 May 1940, German forces defeated Allied forces by mobile operations and conquered France, Belgium, Luxembourg and the Netherlands, bringing land operations on the Western Front to an end until 6 June 1944. Italy entered the war on 10 June 1940 and attempted an invasion of France.

The German plan for the invasion of France consisted of two main operations. In Fall Gelb (Case Yellow), German armoured units pushed through the Ardennes and then along the Somme valley, cutting off and surrounding the Allied units that had advanced into Belgium, to meet the expected German invasion. When British, Belgian and French forces were pushed back to the sea by the mobile and well-organised German operation, the British evacuated the British Expeditionary Force (BEF) and several French divisions from Dunkirk in Operation Dynamo.

After the withdrawal of the BEF, the German forces began Fall Rot (Case Red) on 5 June. The sixty remaining French divisions made a determined resistance but were unable to overcome the German air superiority and armoured mobility. German tanks outflanked the Maginot Line and pushed deep into France. German forces occupied Paris unopposed on 14 June after a chaotic period of flight of the French government that led to a collapse of the French army. German commanders met with French officials on 18 June with the goal of forcing the new French government to accept an armistice that amounted to surrender.

On 22 June, the Second Armistice at Compiègne was signed by France and Germany, which resulted in a division of France, whereby Germany would occupy the north and west, Italy would control a small occupation zone in the south-east and an unoccupied zone in the south, the zone libre, would be governed by the officially neutral Vichy government led by Marshal Philippe Pétain. This led to the end of the French Third Republic. France was not liberated until the summer of 1944.

In 1939, Britain and France offered military support to Poland in the likely case of a German invasion. In the dawn of 1 September 1939, the German Invasion of Poland began. France and the United Kingdom declared war on 3 September, after an ultimatum for German forces to immediately withdraw their forces from Poland was met without reply. Following this, Australia (3 September), New Zealand (3 September), South Africa (6 September) and Canada (10 September), declared war on Germany. British and French commitments to Poland were met politically but they adopted a long-war strategy and mobilised for defensive land operations against Germany, while a trade blockade was imposed and the pre-war re-armament was accelerated, ready for an eventual invasion of Germany.

French soldier at the German village of Lauterbach in Saarland

On 7 September, in accordance with their alliance with Poland, France began the Saar Offensive with an advance from the Maginot Line 5 km (3.1 mi) into the German-occupied Saar. France had mobilised 98 divisions (all but 28 of them reserve or fortress formations) and 2,500 tanks against a German force consisting of 43 divisions (32 of them reserves) and no tanks. The French advanced until they met the then thin and undermanned Siegfried Line. On 17 September, the French supreme commander, Maurice Gamelin gave the order to withdraw French troops to their starting positions; the last of them left Germany on 17 October. Following the Saar Offensive, a period of inaction called the Phoney War (the French Drôle de guerre, joke war or the German Sitzkrieg, sitting war) set in between the belligerents. Adolf Hitler had hoped that France and Britain would acquiesce in the conquest of Poland and quickly make peace. On 6 October, he made a peace offer to both Western powers. Even before they had time to respond, on 9 October, he also formulated a new military policy, in case their reply was negative, "Führer-Directive Number 6" (Führer-Anweisung N°6).[18]

Hitler recognised the necessity of military campaigns to defeat the Western European nations, preliminary to the conquest of territory in Eastern Europe, to avoid a two-front war but these intentions were absent from Directive N°6.[19] The plan was based on the seemingly more realistic assumption that German military strength would have to be built up for several years. For the moment only limited objectives could be envisaged and were aimed at improving Germany's ability to survive a long war in the west.[20] Hitler ordered a conquest of the Low Countries to be executed at the shortest possible notice. This would forestall the French and prevent Allied air power from threatening the vital German Ruhr Area.[21] It would also provide the basis for a long-term air and sea campaign against Britain. There was no mention in the Führer-Directive of any immediate consecutive attack to conquer the whole of France, although the directive read that as much as possible of the border areas in northern France should be occupied.[19][22]

At first, Hitler proposed beginning the invasion on 25 October 1939 but accepted that the date was probably unrealistic. On 5 November, he informed Walther von Brauchitsch that he planned for the invasion to begin on the 12 November. The general replied that the military had largely not recovered from the Polish campaign; the motorised units had to recover, repairing the damage to their vehicles and ammunition stocks were largely depleted. Brauchitsch offered to resign if Hitler did not change his mind. His resignation was refused but two days later Hitler postponed the attack, providing poor weather as the official reason for the delay.[23][24]