TY JOUR TI Exclusivity of federal states and modern theory of federalism KW the federative state KW Montevideo Convention KW exclusivity of the federative states KW constituent entities of a federal state KW Constitution of Bosnia and Herzegovina KW the Union State of Russia and Belarus KW legal status of the Kaliningrad region KW post-Soviet space KW supranationality of statehood JO Vestnik of the St. Petersburg University of the Ministry of Internal Affairs of Russia AU Romaykin, I.A. PY 2026 IS 2026 PB SAINT-PETERSBURG UNIVERSITY OF THE MINISTRY OF INTERNAL AFFAIRS OF THE RUSSIAN FEDERATION