Prohibitive cost of mining these strategic metals, plus a piss poor plan of recycling the raw elements, like copper and lead for bullets. Titanium and molybdenum for hardening steel. Lithium for its reactive, explosive nature.

Military build up focused on big, shiny, new megamachines like carriers, battleships, submarines, bombers, and fighters. The shortage in in materials for their bullets and rockets.

"Gee. I guess we didn't thunk about that."