The Communist Party
One of the most important developments in the 1920s was the rise of the Communist Party, which split off from the Socialist Party in the aftermath of the Soviet Revolution. The socialist movement, influenced by Karl Marx, had been based on the belief that there would be an international revolution of all workers, rising up at once. And in 1919-1920, the success of Lenin's Bolsheviks in Russia was followed by similar uprisings in Germany, Hungary and other European countries.
However, these other uprisings failed to seize and hold power as Lenin's Bolsheviks had done. By 1921, it was evident that there would not be a series of international uprisings. Instead, the new Soviet government began to pursue a policy of "socialism in one country." This meant that the primary goal of the Soviet government would be to ensure its own survival against internal and foreign enemies who wanted to undo the revolution and eliminate "actually existing socialism." The leaders (and many other Europeans) believed that the Bolsheviks (now named the Communist Party) had, by virtue of its successful seizure of power, taken on a historical responsibility to lead all other socialists.