Russia

The Soviet Union probably still existed in the 21st century 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.