What land did Russia lose and gain during WWI and WWII?
in 1918 it lost all its western provinces with the exception only of russia proper but then regained most of lost provinces with the exception of poland,finland,estonia,latvia,lithuania,significant portions of ukraine and belarus ,bessarabia and the kars and ardahan regions in the caucasus.in 1945 it regained all of the areas east of the bug river line therefore all of what was eastern poland according to the 1921 boundaries of poland and also estonia,latvia and lithuania plus a significant portion of eastern finland and also bessarabia plus north bukovina and also transcarpathian ruthenia and lastly the southern half of sakhalin and the kuril islands .
Russia lost Estonia, Latvia, Lithuania, Finland, East Poland and Rumanian Bessarabia in 1919 following the Bolshevik Revolution. These lands were Russian Tsarist Provinces in 1914. In 1939 the Russo-German Pact restored all threse lands which the Red Army occupied from June 1940. Finland preserved its independence 1939-40 during the Winter War causing the Red Army 200,000 casualties.
The three Baltic States, Finland and Rumania allied with Germany to challenge Red Army expansion.
After the Russian civil war and the coming to power of the Bolsheviks, Russia pulled out of the war (WWI) and lost over 25% of its land (and 33% of its population) to Germany (treaty of Brest-Litovsk). Then Poland attacked Russia to gain territory and although they were repulsed the Polish back to Warsaw (where the Polish won the Battle of Warsaw) the Poles pushed back. Eventually a treaty (the treaty of Riga)was signed giving significant amount of land to Poland. Lenin let go so much of the land because he believed (correctly as it turned out) that Russia would reacquire the land once its economy and communism had a firm foothold. All this shows the land lost and gained by Russia over the years, the map of 1920 is the one your looking for.