The Battle of France, 10 May – 25 June 1940, also known as the German: Westfeldzug, German: Frankreichfeldzug and French: campagne de France was the German invasion of France, Belgium, Luxembourg and the Netherlands during the Second World War. On 3 September 1939, France had declared war on Germany, following the German invasion of Poland. In early September 1939, France began the limited Saar Offensive. By mid-October, the French had withdrawn to their start lines. The Germans invaded Belgium, Luxembourg and the Netherlands on 10 May 1940 and Italy entered the war on 10 June. France and the Low Countries were conquered, ending land operations on the Western Front until the Normandy landings on 6 June 1944.
In Fall Gelb, German armoured units made a surprise push 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. British, Belgian and French forces were pushed back to the sea by the German armies and the British and French evacuated the British Expeditionary Force, French and Belgian troops from Dunkirk in Operation Dynamo.