You could argue that it didn't work with North Korea as well (as the regime is still there). But in fact the whole country had been bombed to such condition tha

You could argue that it didn't work with North Korea as well (as the regime is still there). But in fact the whole country had been bombed to such condition that it simply had no buildings left, it had been totally flattened, ~300k civilians dead. Could happen with Ukraine as well if they couldn't eventually counter the Russian air force. https://en.wikipedia.org/wiki/Bombing_of_North_Korea https://en.wikipedia.org/wiki/Bombing_of_North_Korea And Putin would be totally happy with the destruction of Ukraine if they don't submit. Either outcome is good for him.