There was a massive ancient civilization in Illinois. In 1250 the lost city of Cahokia was larger than London. Today more than 120 massive earthen mounds are still located on the site.
Piles of ancient corpses, vitrified rock, and intense radiation have all been observed in the Indus River Valley. While not a mainstream theory, this evidence suggests that the mysterious Indus Valley Civilization was destroyed with some kind of atomic weapon.
Tiny, spiral-shaped metal objects have been found in Russia that have been dated to be around 20,000 years old. Since humans are thought to have discovered metalworking only 6,000 years ago, no one can explain where these objects came from.