The soviets didn't want their postwar reign in Poland to be challenged by the largest and most effective underground resistance of WWII, so they were content to sit accross the Wisla and let the AK and the Germans annihilate each other.

Now about the comment "it's a long way to go to help," think about the convoys going all the way to Russia, and suffering huge losses. If my geography serves me well, Russian Ports on the White Sea were about twice as far.

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