Was Hiroshima the biggest event of World War 2?

Transcript
Extracts from a memorandum on the Atom Bomb from Prime Minister Clement Attlee, 28th August 1945

Catalogue ref: CAB 126/257

Scientists agree that we cannot stop the march of discovery. We can assume that any attempt to keep this as a secret in the hands of the U.S.A and U.K is useless. Scientists in other countries are certain in time to hit upon the secret.
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The only course which seems to me feasible and to offer a reasonable hope of staving off imminent disaster for the world is joint action by the U.S.A., U.K. and Russia based upon stark reality.

We should declare this invention has made it essential to end wars.
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All nations must up give their dreams of realising some historic expansion at the expense of their neighbours. They must look to a peaceful future instead of a warlike past.

This sort of thing has in the past been considered a Utopian [impossible] dream. It has become today the essential condition of the survival of civilisation and possibly of life in this planet.
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