Russia has expanded since the 17th century: The title of the emperor and the territories of which he was the Sovereign does not mention Ukraine or Russia or the peoples who live there. The collapse of the Russian Empire created the USSR and the republics, the USSR was the successor of the Empire and not the USSR.
"By the grace and help of God, We, Nicholas the Second, Emperor and Sovereign of All Russia, Moscow, Kiev, Vladimir and Novgorod, Emperor of Kazan, Emperor of Astrakhan, Emperor of Poland, Emperor of Siberia, Emperor of Chersonese of Tavrid, Emperor of Georgia, Lord of Pskov and great Prince of Smolensk, Lithuanian, Volhynia, Podolsk and Finland, Prince of Estland, Lifland, Courland and Semigallia, Samogitsk, Bialystok, Karelian, Tver, Yugorsk, Perm, Vyatka, Bulgarian, etc., Lord and Grand Duke of Novgorod, Nizhny Novgorod, Chernihiv, Ryazan, Polotsk, Rostovsk, Yaroslavsk, Belozersk, Udorsk, Obdorsk, Kondsk, Vitepsk, Mstislavsk and all the Northern lands Commander, and Lord of the Iversk, Kartalinsk and Kabardinsk lands and territories of the Armenian, Cherkasy and Mountain Princes and others Hereditary Lord and Possessor, Lord of Turkestan, Heir Norwegian, Duke of Schleswig-Holstein, Stormarn, Ditmarsen and Oldenburg, etc., etc., etc. "Where is Ukraine or Russia mentioned here? The USSR was the successor of the Empire, which again means that all the republics were the successor states of the late empire and not only the USSR.