Russia

The Union of Soviet Socialist Republics (USSR) still existed in the 21st century, prior to Great War, in the Fallout world, as Natalia, one of the Fallout 1 pre-made characters, is a grandchild of a Russian diplomat, who worked at the Soviet Consulate in Los Angeles.

It is, however, most likely that it it lost its position of the dominant communist country to China, as it is not mentioned at all in other parts of the background, especially in background concerning the Great War. It is also probable that USSR survived nuclear holocaust, by not taking part in Great War.

Because of Natalia's grandparent presence in the Vault 13 few obvious conclusions are possible:
 * Soviet Union had foreign and consular service, had diplomatic relations with USA and in 2077 year didn't wage war against it,
 * name of the state still confirms its liaisons to communist system (however the name of the state was "tradition" only, soviet means council, not communist),
 * Soviet Union didnt't wage war because of resources deficit in 2077 or wasn't significant party during this war (didn't have to or wasn't able to, however more probably "no GNN news, good news"); without any revolution concerning its transcaucasian, middleasian and siberian dominions it could have sufficient supply with coal, oil and gas,
 * Soviet Union didn't collapsed in twentienth century and could be present before the War as the power in 1945 year borders (however some Soviet Union - China "competition" for Siberia was possible like nowadays),
 * Soviet Union possessed 4 United Nations member states votes, because its "inner republics" Belarus and Ukraine had been UN original members since 1945 year; it was permanent member of The Security Council also, which was connected with veto right,
 * Soviet Union should have its sphere of international influence, which could be the same as Warsaw Pact of 1955 and Comecon agreement of 1949 and could limit eastern borders of the European Commonwealth (members of Warsaw Pact were Albania, Bulgaria, Czechoslovakia, German Democratic Republic, Hungary, Poland, Romania, Soviet Union; members of Comecon were Mongolia, Cuba and Vietnam also),
 * Natalia's grandparent as soviet citizen could afford to obtain place in vault (was rich or commited fraud with soviet state property) and as foreign citizen was able or was allowed to get it the vault (with Soviet Union and US authorities acceptation, which implicate good SU-USA relations, or sneaking in).