Communism as the ultimate phase of Real Socialism requires that Capitalism be eliminated worldwide. Then, the production inefficiencies of Socialism, the lagging innovation and the resulting military disadvantage would no longer be a factor.
In the 20th century, we had two forks leading that at least in theory could give the USSR a chance to establish its control over the entire European continent:
- In 1937–1941, the USSR had the largest army and the most able military-industrial complex in the world. During that time, sympathies for the Communist cause also were at the zenith across the continent. Of course, it remain unclear how the Soviet Union would handle America on the other end of the Atlantic, and Great Britain with their wealth of fallback strategies in the overseas territories.
- In the mid-1970s, the USSR reached the nuclear parity with the US, with the potential for Mutual Assured Destruction as a consequence. In the case of a full-blown nuclear war between NATO and the Warsaw Block, the Communist China, staying out of the fray, would have a chance of enforcing their version of Communist rule on the surviving humanity.