We ask four historians whether the demise of one of the 20th century’s superpowers was as inevitable as it now seems. Soviet poster dedicated to the fifth anniversary of the October Revolution and IV Congress of the Communist International, 1922. Wiki Commons. ‘No one has suggested a convincing alternative scenario’ Rodric Braithwaite, British Ambassador to the Soviet Union (1988-91) and author of Armageddon and Paranoia: the Nuclear Confrontation (Profile, 2017). People still argue about the fall of the Roman Empire. They are not going to agree quickly on why the Soviet Union collapsed when it did. Some think it could have lasted for many years, others that the collapse was unforeseeable. Andrei Sakharov, the Soviet dissident scientist, foresaw it decades before it happened. Victory in war took the Soviet armies to the centre of Europe, where they stayed. The Soviet Union’s seductive ideology had already given it influence across the world. But after Stalin’s death in...