Soviet nationality ceased to exist and most former Soviet Republics adopted their own nationality laws yet the collapse of the USSR is one of the events in recent history that has resulted in mass statelessness.

Was the Soviet Union stateless?

The dissolution of the Soviet Union in 1991 led to large scale statelessness in the Baltic states and Eastern Europe.

Are Soviet passports still valid?

The Soviet passports ceased to be valid as means of personal identification since mid-2004, but it is still legal (though barely practical) to have one. ... Internal Russian passports are issued only inside the country.