Saturday - Christmas Day - marks the 30th anniversary of one of the turning points in the history of the past century: the collapse of the Soviet Union. People strolling across Red Square in Moscow on the evening of 25 December 1991 witnessed the Soviet flag over the Kremlin being pulled down and replaced with a tricolour of the Russian Federation. Just moments before that, Soviet President Mikhail Gorbachev announced his resignation in a live televised address, drawing a line under more than 74 years of Soviet history.