Abstract: The subject of the study is the internal processes in the USPD (Independent Social Democratic Party of Germany), as well as external factors from the spring of 1921 to the summer of 1922, which led to a change in the party's strategy and, ultimately, to its unification with the SPD (Social Democratic Party of Germany). Special attention is paid to discussions on the party's strategy in the conditions of crisis for the Weimar Republic, namely, left-radical and right-radical threats, the difficult foreign policy situation and instability of the party-political system. The research methodology is based on the tools of historical and political sciences. In particular, it is important to use a psychological approach in party science, which implies the study of the NSDPG based on the subjective vision of political and socio-economic processes by individuals, a group of individuals or the whole collective, which allows us to analyze the motivation of the actions of independents. The study demonstrates that in the conditions of the extremely unstable situation in the Weimar Republic and competition with other left-wing parties, the NSDPG's action program became unviable, as a result of which the party became closer to the SPD on many key issues. The novelty of the study lies in the fact that, unlike the Social Democrats and Communists in Germany, the history of the NSDPG has been studied to a much lesser extent. Of course, there is a fairly extensive historiography, however, the authors paid close attention to the reasons for the separation of the party in 1917 and the issues of its split due to the issue of joining the Third International in 1920, while the process of rapprochement between the NSDPG and the SPD was considered superficially.