Take a look at man's ability to deal inhumanity to his fellow men.
Sobering to realize that even the smallest one would do terrible damage and kill a lot of people in an urban area. A Davy Crockett shell would take out a few blocks in New York City; The biggest Russian device tested, the Tsar, would obliterate Manhattan, and irradiate most of Long Island, a big chunk of New Jersey, as well as the southern parts of Pennsylvania and Connecticut.
As somebody who grew up under the threat of mushroom clouds in the duck-and-cover days, and in a city that was on the Russian's Top Ten Hit list I used to have nightmares about nuclear Armageddon. Look at the map of Louisiana, and see what the biggest Russian nuke tested would have done had it been dropped on the oil refineries in Baton Rouge. Third-degree burns halfway to New Orleans, seventy miles away; up to Mississippi, almost to Opelousas and Lafayette.
Einstein had it:
"I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones ..."