Assertion: After the Second World War, the Soviet economy was more developed than the rest of the world except for the US.
Reason: The Soviet Union became a great power after the Second World War.

Both the Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.

The Soviet Union became a great power after the Second World War. The Soviet economy was then more developed than the rest of the world except for the US. It had a complex communications network, vast energy resources including oil, iron, and steel, machinery production, and a transport sector that connected its remotest areas with efficiency. It had a domestic consumer industry that produced everything from pins to cars, though their quality did not match that of the Western capitalist countries. The Soviet state ensured a minimum standard of living for all citizens, and the government-subsidized basic necessities including health, education, childcare, and other welfare schemes. There was no unemployment. State ownership was the dominant form of ownership: land and productive assets were owned and controlled by the Soviet state.