Heck, still a lot of WWI and WWII stuff out there.
Tons of it. Be careful metal detecting around old military bases. The ground might be loaded.
My sister visited the Verdun battlefield in France back in the 70s. While there, the TV carried a report of another farmer killed when his plow hit a WWI shell. She said that after a rain you could see the stuff sticking up out of the ground.
On a slightly different note, again in the 70s, I attended a college symposium by some think tank guys. One person asked why China couldn't lob a nuke at Russia, blame America, and watch the two superpowers destroy themselves.
The guy shocked the audience by saying, "The first bomb is free." You could hear the gasp and I thought WTF? These guys are crazy.
He then explained that we had a reciprocal agreement with Russia not to hit the button if a huge explosion took place on their soil. As a case in point, he said that the Russians were excavating an area jusr outside of Stalingrad in preparation for another block of tenements. In the process they uncovered a vast ammunition dump abandoned by the Germans. He said it contained over 20,000 tons of explosives and that all a bulldozer had to do was hit one of the shells the wrong way with it's blade to create a Hiroshima-strength explosion.