It was not formerly Russian. Hell, Russian Poland was basically what the Austrians and Prussians have them after the Napoleonic Wars. Trans-Carpathian Ruthenia had nothing to do with Russia territorial up until WWII, even if they did call themselves Rusyn and want to join the them,A certain amount of interwar Czechoslovakia was former Russian territory (Carpathia), as well as the issue with its northern border having taken a chunk of Poland in this map.