In Germany after WWI and into the early 1930s Bolshevik activists and the German Communist Party (KPD) engaged in aggressive economic sabotage, street violence and even assassinations. This along with the Great Depression led to German middle class support for the National Socialist Party and the Third Reich (fascism). Much of history's focus is on the horrors of the Nazis, but many people are unaware of the extreme threat of communist revolution in Europe during this era, a threat which was used by the Nazis as a perfect rationale for constructing a police state. Arguably, without the existence of hardline communism, the fascists never would have had the public support needed to rise to power.
In Russia after the Bolshevik Revolution, the Cheka secret police were established in the name of preventing "counter-revolution". This is an interesting aspect common to communism in particular; they desperately cling to the narrative that THEY are the "revolutionaries", even when they have all the power. Thus, the revolution never ends because there are always people who disagree with communism. Anyone who refuses to comply with Marxist mandates becomes an imperialist enemy and bogeyman, and is held up as an example of why the revolution must perpetually continue. The police state must exist forever to root out the evil classists lurking in the shadows.