The Tsar Bomba? It had a blast radius 3 times the size of the entire London Metro area.
The fact that such a destructive weapon was ever built
by Humans is enough for me to believe we will, eventually, accidentally or not.... destroy ourselves. Of course during the Iraq War we wanted a fun bomb to scare the crap out of Iraqi's while flattening entire city blocks, so we invented the MOAB (Mother of all Bombs) with an 11ton yield..
So, naturally, Russia built the FOAB (Father of all Bombs) with a 44ton yield.. which is about the same size as our newer small tactical nukes.. Perhaps eventually we won't even need nukes since we keep finding more compact, cheaper and easier to maintain high explosives.
But to answer my own question as to why we would use smaller nukes.. en.wikipedia.org... We apparently invented a nuke that launches into space then carpet bombs a target with smaller nukes, actually creating more damage than a large nuke (except of course the megabombs)



