On January 19, 1951 (entry into force of the Polish Citizenship Act of 1951), Polish citizens of nationality:
who lived permanently abroad lost their Polish citizenship.
A similar rule applied to Polish citizens of German nationality, unless the spouse has Polish citizenship and lives in Poland.
Loss of citizenship concerned not only Polish citizens who remained after the Second World War in the USSR, but all citizens of the above-mentioned nationalities living abroad. For example, Polish citizenship was lost to people of Ukrainian nationality living in the USA or in Argentina.