There are differences — to confuse them is to misread history.
The differences were superficial and ideological. Practically Stalinism and Nazism were practically identical. Stalin himself broke with the “International” Socialism (Trotsky) and became a “National Communist”. Nazism in essence is Socialism crossed with Nationalism and Racism (which lacks in international communist ideology(. The methods, the rethoric (the one says class, the other says race), the goals and the cost in human lives were identical.