In 1920, the ultra-lefts of this party, mainly consisting of council communist members whose origins lay in the ISD, split from it to form the KAPD.

The KAPD especially rejected the Leninist form of organisation along with democratic centralism, participation in elections, and activism within reformist trade unions, unlike the KPD.

In August 1920, the founding members of the Hamburg branch were expelled, Heinrich Laufenberg and Fritz Wolffheim, who had advocated National Bolshevist ideas.

This was triggered by Weimar Republic troops marching into the industrial region of Central Germany, and the KAPD and KPD's fear that the military intended to occupy the factories.

In 1921 a further fragmentation occurred, when parts of the AAUD around Rühle, Franz Pfemfert and Oskar Kanehl broke off from the KAPD and formed the AAUE.

The main reason was the Essen Faction's rejection of participation in workers' struggles in factories, in a situation seen as revolutionary.

A section led by Otto Rühle, based in Essen, split from the AAUD, forming the General Workers' Union of Germany – Unitary Organization (AAUD-E).

[6] The delegates of the KAPD to the 2nd World Congress of the Comintern were scorned and their speeches were restricted to a mere ten minutes.

This was following the publication of Lenin's Left Wing Communism, which was written as a critique of the left-wing ideas of the KAPD, among other left-communist parties, including the KAPN.

[8] Historian E.H. Carr has argued that the 2nd World Congress—to some extent unintentionally and unconsciously—was the first to "establish Russian leadership of Comintern on an impregnable basis.

[10] Amadeo Bordiga, leader of the Sinistra in that time, who met members of KAPD in person in Berlin on his route to Moscow, in a 1926 letter to Karl Korsch he was skeptical of any joint action between the two lefts because of fundamental political divergences and stated: (...) We agree with Lenin's theses [on the Party's role] at the 2nd Congress.