Lenin wished to spread Communism around the world and initiate a worldwide revolution, with the eventual aim being that the workers would break beyond their borders (having more in common than mere race, language or nationality), and lead to a dictatorship of the proletariat. This was demonstrated by the establishment of the Comintern in 1919 (to spread Communist influence), and being heavily influenced by the works of Marx and Engels (such as Marx's Labour Theory of Value).
After his death in 1924 however, this was debated within the Politburo, and Stalin, after coming to power in 1928, focused on autarky and "socialism in one country" through the creation of a totalitarian state. So if there were to be a "turning point", it would be the death of global Communism's biggest advocate at the time: Lenin himself.
Hope it helps!
Sources -
Lenin: A Biography, Robert Service. http://books.google.co.uk/books?id=N9mbl_xbWpkC
In terms of the global presence of communist movements, I think that one fact that is often overlooked is the huge influence that Marxism/Leninism had in the Third World and in the decolonization movements. Take Africa, for instance; the decolonization struggles in Angola, Mozambique, Guinea-Bissau, South Africa, Zimbabwe, and Algeria were all various shades of Marxist. The book Postcolonialism: An Historical Introduction does an excellent job of looking into the massive influence that Marxism and revolutionary communism had on the decolonization struggles of the 20th century that involved the majority of the world's population, and the "tricontinental" (Latin America, Africa, Asia).
Also, I would caution against seeing communism as something that has already been "prevented". There are plenty of communist or Marxist-inspired movements in the world today (South Asia, Venezuela, South Africa) that are arguably on the upswing, although discussing this would break the 20-year rule of /r/AskHistorians.
Sorry, but your submission has been removed because we don't allow hypothetical questions. This sort of thing is better suited for /r/historicalwhatif.