About the initial post:

The nuclear Bombing Japan was not mainly pursued to end the war or whatever.
The main purpose was to show off the magnitute and effectiveness of the bombs.
(In fact, the bombs where in production for years,
and where initially thought to be used against Germany.)

The second bombing was to test the difference between
Uranium and Plutonium designs.

Add some propaganda and Hollywood movies, and the bombing
is regarded "nessesary" in the US.

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In the end, using the V2 Rockets by Germany had the same
intentions. it was a new technology, used to show off and scare opponents.
Its a war logic, but its not "moral" by todays understanding.