The Mäntsälä rebellion occurred in the context of a heightened atmosphere of political polarization in Finland during the early 20th century. The Lapua Movement, a far-right nationalist organization, had gained considerable following by promoting anti-socialist sentiment and championing conservative values. On that day, as social democrats gathered to discuss their political agenda, the Lapua Movement members took to violent confrontation to disrupt the meeting, marking a serious escalation in their campaign against perceived leftist threats. This attack involved armed members who shot towards the assembly, creating panic and chaos among the attendees.

The backdrop to this incident included the economic turmoil of the 1930s, which intensified class struggles across Europe. In Finland, the Lapua Movement sought to capitalize on these tensions by presenting themselves as protectors against leftist influences. Their action in Mäntsälä served to galvanize both the right and left, leading to an increase in organized political violence. Social democrats and left-wing factions faced severe risks as they fought for their rights and representation in a rapidly polarizing society.

The aftermath involved increased security measures at political gatherings, a crackdown on extremist groups, and ultimately, a shift in Finnish politics. As political violence became more commonplace, the government was forced to reconsider its stance on civil rights and public safety in the face of an increasingly radicalized citizenry. The Mäntsälä rebellion thus not only highlighted the immediate conflict but also set the stage for significant changes in Finland's political landscape, as leftist and rightist factions would continue to vie for supremacy in the ensuing years.