Not only did the Germans attack in a place thought totally unsuitable for armor, but they used their armor in unexpected ways, driving deep into the French interior without waiting for the infantry to catch up. They also used their aircraft as long range artillery to neutralize the French artillery which had been placed so as to be out of range of German artillery but able to bombard any attempted river crossing. Once the river was crossed, the French artillery could be engaged by German infantry and light armor. German armor then penetrated deep into the French interior. Strategic defenses are stabilizing, not destabilizing, because they are dangerous only to the aggressor.
Strategic defenses make strategic offense weapons obsolete.