Final answer:
The Ardennes was considered France's weakest link during World War II because of the strategic oversight regarding the forest's passability and the assumption that the Maginot Line's fortifications would deter German aggression. Coupled with the French miscalculation of the speed of German mobilization and the effective use of blitzkrieg tactics, it left France vulnerable to the swift German invasion in May 1940.
Step-by-step explanation:
The Ardennes was considered the weakest link for France during World War II largely due to strategic miscalculations and assumptions made by the French military command. The Maginot Line, a system of formidable fortifications, was thought to be impenetrable and consequently, the area of the Ardennes Forest was left less defended as it was considered a natural barrier. This underestimated the possibility of a German attack through this area. Additionally, the French military strategy was not prepared for the rapid German mobilization and the effective use of tanks and motorized infantry in their blitzkrieg tactics.
The French had extended the Maginot Line along the German-French border but did not continue it through the Ardennes to avoid alienating their Belgian ally. The line's absence in the Ardennes, combined with the French misjudgment of the forest's passability, left France vulnerable to the unexpected and swift German advance through the region. When the Germans did invade the Netherlands and Belgium, they sent their main force through the Ardennes, quickly penetrating French defenses and rendering the Maginot Line irrelevant as it was bypassed.
This failure to match the speed and innovation of the German's military strategy ultimately led to a rapid defeat for France when the Germans attacked in May 1940, a defining moment at the outset of World War II in Western Europe. The collapse of Allied morale and the lack of preparation for armored warfare further sealed the fate of France, as they were unable to effectively counter the German strategy.