Last century had two major wars that redrew the map of Europe, one that redrew Africa, two in Asia, and one that completely changed eastern europe.
On top of that, war has left lasting signs dotted around Europe, vast political wakes, and changed the world entirely.
In Britain, you literally cannot walk 10 miles without coming across something left over from WW2. The town I grew up in was built around an airfield and a factory, and one end of town was dotted with old fortifications.
The bottom of the Atlantic is dotted with the remains of very similar ships, and so are the waters around Japan and the various chunks of pacific islands.
Take a geiger counter to a scrapyard and you'll find evidence of war. They focus on it with good reason, the only reason we aren't still killing each other in huge bloody wars is because it would literally kill everybody.