State socialism
State socialism is a nebulous political and economic concept which involves the state ownership of the means of production on behalf of the proletariat with the ultimate goal of transitioning to a more democratic socialist system of control. The term state capitalism is sometimes used interchangeably with this concept, however if there is a difference to be made, then state capitalism refers to state ownership without the intent to transition to socialism later on. Democratic and libertarian socialists in particular tend to use these words interchangeably, as they generally tend to view state socialism as actually just partially socialist. In contrast, it may be said that workers in state socialist nations have genuine control over the means of production through institutions such as trade unions, and thus state socialist nations in practice really are essentially socialist.
Discussion
Supposed tendency for state leaders to grow corrupt, making socialism unattainable through state means
The governors of the Soviet Union, for instance, from the beginning ruled rather democratically. The Bolsheviks ruled as part of a coalition government that was fairly moderate, however the Civil War and intervention by imperialists forced their hand to become more strict; however, there was still a Congress and other checks to the power of a General Secretary, or otherwise that of the leader. The Soviet Union was not unreasonably cruel for the sake of cruelty, but rather exerted controls appropriate to the circumstances. To quote William Blum:
History does not tell us what a Soviet Union, allowed to develop in a 'normal' way of its own choosing, would look like today. We do know, however, the nature of a Soviet Union attacked in its cradle, raised alone in an extremely hostile world, and, when it managed to survive to adulthood, overrun by the Nazi war machine with the blessings of the Western powers. The resulting insecurities and fears have inevitably led to deformities of character not unlike that found in an individual raised in a similar life-threatening manner.
— William Blum, Killing Hope, Introduction
Leaders were not all-powerful and frequently had their wishes rejected by other powers in the government; even Stalin, who had for instance once nominated Kaganovich for head of civil aviation, however the Politburo had decided instead on Goltsman. Another instance was when Stalin had proposed Malenkov to be the Commissar of Internal Affairs following the downfall of Yezhov yet the Politburo once again decided otherwise; opting for Lavrentiy Beria for the post. Stalin was further rejected in many of his bids to reform the political system, indicating that no one, not even someone called the leader of the Soviet Union, and someone holding several political offices concurrently, could exert full control and act as they would please.
Throughout the history of all the socialist states, collective leadership has been the norm, overall. Where this did not occur was either due to historical factors (e.g. the promotion of Stalin due to the need to promote unity and due to lack of experience in constructing socialism) or departures from Marxism-Leninism (e.g. Ceaușescu's national communism, Mao's "Great Proletarian Cultural Revolution"[tendency-based slant]). In such cases it does not matter how many parties exist.
In the USSR, all major decisions were voted upon democratically in the Politburo, which later went to the Central Committee for confirmation. This was a practice that started with Lenin, and both bodies convened regularly after Stalin's death. Brezhnev had less power, for example, than an American president, due to the control exercised by his peers.