In recent years declassified documents have provided some very interesting secret developments uncovered regarding WWII.
First off, MI6 ran covert operations inside the US aimed at political and civilian isolationists alike, and succeeded brilliantly in many cases.
Starting at 16:19 we see examples of this, culminating with a forged German map showing their intentions in South America -
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As you saw, Roosevelt was furious a year later when the deception was uncovered, but was persuaded that revealing the information would be detrimental to all concerned.
Is this secret act of deception to be considered a betrayal of the trust between these two countries?
Perhaps.
But in hindsight, in light of new information it might be construed as a well needed nudge into action against a very real threat of proportions America was still oblivious to.
Information released since the war has shown that with a little more time new German wonder weapons would have decimated Allied troops and Air Forces.
Now consider the fact that Japan had it's own Manhattan Project, and were much further along than even the Germans -
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So once again, with a little more time it would have instead been the Allies facing the brunt of new technology.
...and amazingly, the Japanese were prepared to keep fighting despite the Atomic Bomb attacks. They were considered not much worse than the firebomb raids that they had already been enduring.
And the military were prepared to impose martial law and carry on fighting, undoubtedly hoping to fire back with their own Atom bombs in short order -
http://apjjf.org/-Tsuyoshi-Hasegawa/2501/article.htmlThey even attempted a Coup to stop the Emperor's surrender broadcast.
So in the end it appears that MI6's nudge to start taking the World War seriously came just in the nick of time.