Importance. An interest in the history of the Civil War in Russia, in which there are many “white spots” is presented. These include the participation of the Czech-Slovak corps in the foreign intervention in Russia and the nature of its relations with the anti-Bolshevik forces. In the summer of 1918, the Czech-Slovak corps, waging an active struggle against the Soviet government, seized control of the Trans-Siberian railway. The numerical superiority over the local Bolshevik forces, the best training, preparation, suddenness of the advance, as well as the enthusiasm of the legionnaires allowed them to take over a number of large cities in the Volga region, the Urals, Siberia and the Far East in a short period of time. This in turn led to the formation of local anti-Bolshevik forces – the Committee of Members of the Constituent Assembly (KOMUCH) and the Provisional Siberian Government in Omsk. Research methods. A historical and systematic method was used to identify the role of the Czech-Slovak corps in the escalation of the Civil War in Russia, taking into account the “Czech-Slovak factor” in international relations of that time. Results and Discussion. Based on a thorough analysis of documents and directives prepared by the Bolsheviks, anti-Bolshevik forces, allies in the Entente, the military and political leadership of the Czech–Slovak corps, it is shown that the corps pursued its goal – to get to Vladivostok, to achieve which the seizure of cities and the overthrow of Soviet government were carried out. At the same time, contact was established with local cells of Social Revolutionaries mainly through commerce. In addition, in relations with the allies, the corps continued to pursue its goals, helping the People’s Army of the Committee of Members of the Constituent Assembly until the moment when it ceased to meet its interests. It is stated that the corps was involved in foreign intervention, since its successes in the struggle against Soviet government forced the Entente countries to reconsider its role in Russia. Conclusion. The Czech-Slovak corps not only initiated the “sharp” stage of the Civil War in Russia, but also became a catalyst for a number of processes both in Russia and in the world that led to further escalation of the conflict.

May 1918 is a turning point in the relationship between the Bolsheviks and the Czech-Slovak Corps. The events that have taken place will lead to the outbreak of a Civil war in Russia, which will take millions of lives. The study of these events currently continues to remain relevant, caused by the appearance of new documents. The Chelyabinsk incident and the organized mutiny of the corps that broke out after it on May 25 were the final stage of relations between the two sides, which began to develop even before the events of October 1917. There is still no exact answer in the scientific community as to what exactly caused the mutiny. The importance and relevance of the study is due to the study of the role of factors affecting the relationship between the two forces, as well as those that made the conflict between them inevitable, in addition, new documents have been attracted that will help give a clear answer to this question. A quantitative analysis of documents and directives prepared by both the Bolsheviks and the political leadership of the Czechoslovak National Council was carried out. The influence of the Brest Peace on the relations of the two forces and its perception by the leaders of the Czechoslovak National Council and the commanders of the Czech-Slovak Corps is analyzed. The main purpose of the study is a detailed analysis of the events of May 1918. The analysis of the “Chelyabinsk incident of May 14, 1918” and its consequences is carried out. It was proved that the mutiny of the corps was a pre-planned action organized by the commanders of the Czech divisions. It is concluded that the signing of the Brest Peace with the Central Powers was a critical moment in the relations between the Bolsheviks and the Czech-Slovak Corps, after which an armed conflict between the two forces became inevitable.