This is an old theory that doesn't hold up at all. The Maginot line was a good investment and worked as intented. And it was by no means as large an investment

This is an old theory that doesn't hold up at all. The Maginot line was a good investment and worked as intented. And it was by no means as large an investment as people claim. Where they failed is in terms of their officers, command&control and training. The French Generals made some horrible mistakes and never managed to recover.