Final answer:
The Germans invaded France through Belgium and Luxembourg, sidestepping the heavily fortified Maginot Line by rapidly advancing through the Ardennes Forest. Utilizing their mobile 'Blitzkrieg' strategy, they caught the French and British forces unprepared, leading to significant Allied retreats.
Step-by-step explanation:
The Germans circumvented the heavily armed French border, known as the Maginot Line, by invading through Belgium and Luxembourg. This strategy involved a rapid advance through the Ardennes Forest, a region which the French and British forces assumed was too dense for a large-scale offensive. The Germans initiated their attack on May 10, 1940, quickly overcoming Denmark and Norway before turning their focus on the Netherlands, Belgium, and France, thus bypassing the French Maginot Line.
The German strategy during this phase of World War II was characterized by a highly mobile form of warfare, known as 'Blitzkrieg,' which emphasized the use of tanks, motorized infantry, and air power to achieve quick and decisive victories. The French, whose military doctrine largely revolved around static defense, were unprepared for the speed and flexibility of the German assault. As a result, the Allied forces were pushed back, leading to significant losses and the eventual evacuation at Dunkirk.