I was in Belgium last year (visiting where dad fought at Elsenborn Ridge[0]) and something I was curious about - after Belgium had been occupied in WW-I, and it became obvious during the inter-war years[1] that Germany was rearming, why didn't they launch a crash defense program?

With Russia now becoming increasingly aggressive, I would think the time to prepare a deterrence is now.

[0] https://en.wikipedia.org/wiki/Battle_of_Elsenborn_Ridge [1] https://www.youtube.com/watch?v=oxkk8CuejV4