What we historically call the "Red Biennium" refers to the two-year period of 1919-1920, when the Italian peninsula, especially the north, appeared to be tightly controlled by a network of unions, peasant/worker associations, and municipal administrations under the Italian Socialist Party. This socialist political influence often resulted in unjustified and counterproductive interference in the production systems of some regions and the affairs of private companies.

The main weapon of socialist political organisation in the postwar period was the strike, which was also used extensively as a means of pressure to force company owners and managers to accept conditions that, from their perspective, were enormously disadvantageous. The occupations of industrial buildings were always accompanied by armed militias of workers, which allowed for defence against attempts by the police to break up the strike, but also caused widespread intimidation among civilians and the growing fear of a possible civil war.

To fully understand these feelings, we must take into account the widespread violence that was developing in Italy with the return of veterans from the front. These veterans, having organised themselves in various ways depending on their political orientation, had begun to bring to the streets what had previously been discussed only in Parliament and decided at the ballot box. The Socialist Party's impact on this postwar political landscape was decidedly unpredictable, with membership rising from 23,000 in 1918 to 200,000 in 1920, while that of the socialist trade union, the CGdL, increased from 250,000 to 2,150,000.

These numbers, combined with majorities in Parliament and in the country's municipal administrations, paint an Italian political landscape that, even for many at the time, resembled the Bolshevik revolution's expansion across the country. The only thing that could have stopped this, in truth, was the internal divisions within the left itself, with the various maximalists, reformists, and anarchists who avoided forming a common front against the other political forces. The final blow was the defeat of the Red Army in Poland, which brought a sense of disorientation to communist groups across Europe and opened the door to action for all anti-communist groups.