Explanation: In January 1919, the Weimar Republic, born only a few months ago from socialist revolutionaries who overthrew the old German monarchy and negotiated an end to WW1, experienced an attempt to overthrow it - the Spartacus Uprising. The initial government was dominated by the SPD - a long-established party of Social Democrats and Democratic Socialists in Germany - and organized elections to be held in Germany in late January, in which the KPD - the German Communist Party, split from the SPD several years earlier - was able to participate.

Participation was not enough for the KPD. Thinking that they could take power without having to bother with ‘bourgeois democracy’, they opted at first to call for a demonstration against what they (and many Berlin workers) saw as overreach by the SPD-dominated provisional government. As turnout was greater than expected, many radicals believed that not only would they be able to bypass ‘bourgeois democracy’ with their current strength, negotiating power-sharing through a general strike, but that they could outright seize the government entirely through force of (the People’s™) arms. They made a call to violence, and to overthrow the provisional government of the socialists in the SPD.

Rosa Luxemburg, a prominent member of the KPD, voted against the insurrectionary idea, despite not being the biggest fan of ‘bourgeois democracy’ herself. She pointed out that the KPD could not take power in either way without the support of a majority of the working class - something which they did not currently have. Her position was the minority in the KPD, but not, it would seem, the minority position of German workers, whose demonstrations very quickly changed from anti-SPD to shaming the KPD as well for endorsing a fratricidal war between the working class.

The SPD and KPD attempted negotiations again at this point, with the provisional government demanding the SPD newspapers that were occupied by KPD partisans be allowed to resume operations, and the KPD demanding the reinstatement of the chief of police in Berlin, whom the SPD believed to have cooperated with the KPD in a military kidnapping-turned-bloody back in December. Neither side budged.

Fighting broke out, and the SPD’s government forces - assisted by right-wing paramilitaries formed of recently-discharged WW1 veterans, ‘Freikorps’, who answered more to their officers than the central government - would win without much serious fighting. Unfortunately, the bloodshed would not immediately end there, as the aforementioned right-wing Freikorps took the opportunity to murder numerous leftist activists in Berlin before they could be transferred to government holding, including Rosa Luxemburg.

The KPD, in-line with its anti-electoralist stance so-decided during the Spartacist Revolt, decided to boycott the first elections of Weimar Germany a week later, leading to a voter turnout of 83%, and left-wing parties in the legislature acquiring 46% of the vote. In other words, just under a majority for the most important constitutional negotiations of the newborn German republic’s life.

Good going.

The Freikorps would be disbanded at the point of a gun after the Weimar government found its initial footing, but the uneasy truce between the (largely conservative and right-wing) army and the (generally left or liberal) civilian government never really resolved itself. The KPD would eventually cooperate with other socialist parties throughout the first half of the 1920s, resulting in some left-wing gains, but the KPD would again reverse to an anti-SPD position under the tenure of Ernst Thalmann, a KPD party leader who closely followed the orders of the Soviet Union’s strongman at the time - Joseph Stalin. This sorry state would eventually lead to the rise of the Nazis as the ineffectual liberal-conservative governments of Weimar Germany flailed about and the SPD failed to win an outright majority without the need for a broader coalition - which the KPD was not willing to offer.