Disaffected Czechs and Slovaks captured from the Austro-Hungarians were recruited into a Czechoslovak Legion to fight alongside the Russians against the Central Powers. The Bolsheviks had agreed to transport the Legion by rail to Vladivostok, from where they would be shipped to Europe to continue their war. However clashes between the Czechoslovaks and the Bolsheviks have seen members of the Legion take over the town of Chelyabinsk, cutting the Trans-Siberian Railway.
Now Trotsky, commander of the Red Army, decides that he has had enough of these troublesome Czechoslovaks. Repudiating the transit agreement, he telegrams Soviets across Siberia, ordering them to suppress the Legion. “Every armed Czech found on the railway is to shot on the spot!”, he demands.
The Czechoslovaks are a disciplined and well-armed fighting force, while the various Soviets still have only Red Guard militia units at their disposal. Trotsky may perhaps have bitten off more than he can chew, initiating an unnecessary war in Siberia that his men will not easily win.
Czechoslovak legionnaires (SovietJournal: The Czech Legion)
Leon Trotsky (Wikipedia)