"The A-bombs were quite unusual. They were extraordinary weapons, and would have required extraordinary justifications to use on the military, let alone on civilians."
Extraordinarily efficient, one plane, one bomb, one city, but we'd already methodically bombed pretty much every other city (along with Kyoto for political reasons, the A-bomb targets and their alternates were reserved), with e.g. the firebombing of Tokyo killing a conservative 100,000.
To view anyone in Japan, or more accurately, anyone in any of the great powers as a "civilian" during the wartime of WW2 - is pretty naive. All of Europe, Japan, and America were in a state of Total War - Every available resource was being put towards the production of munitions, every able-bodied man was being drafted, every spare cent was being spent on the war.
If you want to bomb a target smaller than a city then you have to design smaller bombs.
If you want to target cities then you keep making city-sized bombs.
If you want to target larger areas, you're probably going to be most efficient by targeting the cities in that area; go back to the previous step of city-sized bombs.
What's the incentive to increase lethality? If you make huge nukes or equivalently powerful weapons, they overkill your target and have negative side effects back on the homeland.
Even sub-city-sized weapons like the ones dropped on Japan are too large to actually launch in the modern world; the political repercussions are much too great. The only use for a nuclear arsenal is to promise Mutually Assured Destruction, and it really doesn't take much for that.
The dangerous super-weapons of the future are small, simple ones that can kill just the right person, anywhere, anytime. That arms race is happening right now, and progress is rapid.
Since at least the Napoleonic Wars, which followed shortly after our Revolutionary war, artillery has generally been the biggest killer on the battlefield.
Extraordinarily efficient, one plane, one bomb, one city, but we'd already methodically bombed pretty much every other city (along with Kyoto for political reasons, the A-bomb targets and their alternates were reserved), with e.g. the firebombing of Tokyo killing a conservative 100,000.