So let's say I am on their side (that makes me a bloody nazi) and I know the future.

I would tell him to take it easy on the jews, thus his ideaology would have more supporters in the future.

I would also recommend him to keep good relations with Russia (I know it sounds silly) thus preventing his military force from being annihilated. Then the World would be a tri-polar place.

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"The victor will never be asked if he told the truth."
A.H.