The atomic bomb made wars between nations absurd, but rather than keep the nations and lose the war we preferred to keep the war and lose the nations.
“Atomic bomb” is a synecdoche for the whole package of modern war: poison gas, trenches, Krupp guns, firestorms, machine guns, etc.
Why could we agree to stop using poison gas but not to stop using machine guns or even rifled barrels? Why not agree to use no guns at all? Let both sides meet on a field with lances and horses and farming tools. But if it came to that, we’d never cease from wars. In this sense, we want the technology to save us from war. But this is a pointless thing to want.
If technology made wars ridiculous, then technology ought to be abandoned. Political entities cannot live without war and so we must either choose to exist in such a way that allows war to be a path to virtue or we will be existing in a way contrary to human happiness. Pacifism isn’t just naive, it’s contrary to social well-being.
One city with a big enough bomb could level another, but instead the city advances or retreats against its own occupants, whether we’re talking about the occupants of Baghdad in 2004 or of Paris today.