Maybe the challenge for France going defensive is then not to win, but to make Germany pay the highest possible price before they win, thus helping the global war effort.
If Germany lose some material, but more importantly a fair amount of manpower, they will be hindered when continuing the war.
I agree.
There are at least three goals to playing France even if you think you will lose. (Use them together if you like)
1) Make Germany's victory so painful in terms of manpower that they are unable to invade anyone else or even resist invasion from across the Channel.
2) After making German victory as painful as possible, turn around and make the French Resistance a terrible thorn in the side of the Axis. (In HOI3, I did launch a mass uprising in France 30 days after Barbarossa just to troll Hitler. We lost, but it was epic watching units shift from the Eastern Front to France, including Guderian for some reason.)
3) Drag out the Battle of France so long that Britain can get more assets in place and the US can fire up more Lend-Lease. The longer the Battle of France lasts, the more painful it is for Germany overall in terms of equipment AND (hopefully) Germany generates more threat, getting the US in the war faster. (This assumes battles generate World Tension like they generated Threat in HOI3.)
The disadvantage to France wearing Germany down while losing is that a weakened Germany will be open to attack from the Soviets. You might go down fighting as France and take half the Germany army with you, but then Stalin turns Europe Communist as a result of your tenacity.
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