Why was the Second World War an integral and at the same time a decisive part of the Second World War?

At the beginning of the Great Patriotic War, Nazi Germany in Europe had essentially only one opponent – the USSR. The destruction of the Soviet Union as a state entity would allow the Germans to completely subjugate Europe. Given the critical situation in the UK, it would only be a matter of time before it collapsed.

The war with the USSR destroyed all the power of the Wehrmacht, brought to naught all the resources of Germany. Hitler lost 75-80% of his manpower on the eastern front, and the victory of Soviet soldiers at Stalingrad can be safely considered a fundamental turning point in the entire world war.