In the second of a series of articles marking the outbreak of World War II 70 years ago, historian Orlando Figes analyses what the Molotov-Ribbentrop Pact meant for Europeans in 1939 - and what it means today.
Seventy years on, the pact between Hitler and Stalin still casts a shadow over Europe. Its memory continues to divide.
For the Poles, Lithuanians, Latvians, Estonians and Bessarabians, the pact began the reign of terror, mass deportations, slavery and murder which both the Nazi and the Soviet armies brought along with them when they co-ordinated their invasions of these countries in line with the pact's notorious secret protocols - by which Stalin and Hitler had agreed to divide Eastern Europe between their regimes.
For the Jews of all these lands, the pact was the licence for the Holocaust. For the European Left, the idea that the leader of the USSR could sign a pact with Hitler symbolised the moral bankruptcy of the Soviet regime.
For a long time, apologists for Stalin tried to rationalise his ideological turn-around as a pragmatic necessity to "buy time" for the Soviet Union to arm itself against the threat of Germany.
Certainly, by the summer of 1939, Stalin had good reason to be sceptical that France and Britain were serious about a military alliance with the Soviet Union. The Poles' understandable refusal to allow Soviet troops on to Polish soil was the major stumbling block. This drew the Soviet leader towards Hitler's offer of security.
But Stalin did not see this as buying time for the war with Germany that finally occurred in 1941.
He made no distinction between the liberal capitalist states and the fascist dictatorships - both were enemies.
Through the pact he thought to play them off against each other by giving Hitler a free hand to invade Poland and go to war against its Western allies without intervention by the Soviet Union.
"We are not opposed to war [between Germany and the Western states] if they have a good fight and weaken each other," Stalin said in 1939.
Still an embarrassment
Alongside the pact itself - signed by German Foreign Minister Joachim von Ribbentrop and his Russian counterpart, Vyacheslav Molotov - were the secret protocols. For many years afterwards, the Soviet Union denied their existence.
For many, the pact began a reign of terror, deportations and murder
It was only in 1989, after mass demonstrations to mark the 50th anniversary of the pact, that a Soviet commission finally acknowledged their existence - though the document itself was not published in Russia until 1992.
The pact remains an embarrassment for those in Putin's Russia who take pride from the Soviet achievement in the war.
Its commemoration is a constant thorn in Russia's relations with its neighbouring European states, which, not surprisingly, recall the pact from the perspective of Soviet oppression after 1945.
The European Parliament has called for 23 August to become a day of remembrance for all the victims of the totalitarian regimes - Hitler's and Stalin's. It is not a bad idea.
Perhaps it would help to ease the tensions that are still created by the memory of the pact.
Orlando Figes is Professor of History at Birkbeck College, University of London. He is the author of many books on Russian history, the latest of which is The Whisperers: Private Life in Stalin's Russia (2007). His books have been translated into more than 20 languages.