Although the first program of the Bolshevik movement in Russia included a demand for the "abolition of passports",[23] just two months after the Russian Revolution of 1917, the new regime instituted passport controls and forbade the exit of belligerent nationals.[24] The reasoning was partly that emigration was conflated with opposition to the socialist state and also the fear that emigration would inflate opposition armies.[24] The 1918 Treaty of Brest-Litovsk obligated Russia to allow emigration of non-Russians who wanted German citizenship, but the regime attempted to reduce this flow by allowing it during only one month.[24] Beginning in 1919, travel abroad required the approval of the NKVD, with the additional consent of the Special Department of the Cheka added in 1920.[24] In 1922, after the Treaty on the Creation of the USSR, both the Ukrainian SSR and the Russian SFSR issued general rules for travel that foreclosed virtually all departures, making legal emigration all but impossible.[25] However, the Soviet Union could not control its borders until a system of border guards was created through a special corps of the Gosudarstvennoye Politicheskoye Upravlenie (GPU), such that by 1928, even illegal departure was all but impossible.[25]