The innevitable dialectics of history, and therefore the innevitable victory of socialism consists of two factors: 1. The developement of class consciousnes and 2. The developement of the productive forces, and the ever shorter growing cyclus of crisis.
The farer the productive forces develope and the shorter the cyclus of crisis grows, the more likely the developement of class consciousnes becomes, and therefore the more likely the proletarian revolution becomes.
This goes on untill the point, when the revolution becomes innevitable.
But the timeframe of this happening could be very variable. And this process can even be temporarily reversed. Just look at the german and hungarian socialist revolutions of 1919. These revolutions were defeated, though socialism would still triumph innevitably in those countries.
Now, lets immagine this on a world scale.
Lets immagine, somehow the socialist nations fall back to capitalism and the US becomes the sole superpower. How could this come to be? How would todays world be? Which countries would the NATO states attack after the socialist world fell? How long would it take untill socialism would triuph eventually?