The 1939 Nazi-Soviet Pact is controversial even today, with historians divided over its importance. In the first of a series of articles marking the outbreak of World War II 70 years ago, the BBC Russian Service's Artyom Krechetnikov and Steven Eke analyse the significance of a treaty that helped set the scene for war.
The pact led to the carving-up of parts of eastern Europe
Signed on 23 August 1939, the Molotov-Ribbentrop Pact was accompanied by a secret protocol that detailed the reshaping of Europe's map.
Substantive talks on forming a political alliance between Nazi Germany and the USSR had begun that month.
They built on earlier discussions aimed at boosting economic co-operation, and were accompanied by military and even cultural co-operation in the form of exchanges of high-profile delegations.
The pact was signed by German Foreign Minister Joachim von Ribbentrop and his Russian counterpart, Vyacheslav Molotov, in Moscow.
It led to the carving-up of Poland between Nazi Germany and the USSR, as well as the annexation by the USSR of eastern Finland, Estonia, Latvia, Lithuania and northern Romania.
The western parts of Ukraine and Belarus, formerly Polish territory, were also incorporated into the Soviet Union.
At that point, believe some historians, a war in Europe became unavoidable.
Why Russia signed the pact
Soviet historical approaches currently in favour with Russia's modern-day leadership suggest the treaty:
- Allowed the USSR to delay the onset of war with Nazi Germany
- Allowed the Soviet border to be moved 200km or more to the west, greatly boosting the subsequent defence efforts against Nazi aggression
- Allowed Russia to take under its defence the "blood-brother peoples" - the Ukrainians and Belarussians
- Prevented an "anti-Soviet alliance" between the West and Nazi Germany
The records of the politburo meeting held on 19 August 1939 show that Stalin believed that war with Germany could be avoided, should the USSR form an anti-Nazi alliance with Britain and France.
But, he warned, "the subsequent development of events after that would be unfavourable to the Soviet Union".
He told his colleagues that Germany was prepared to offer the USSR "complete freedom of action in the three Baltic countries", and hinted that Romania, Bulgaria and Hungary would be ceded to the USSR as a "zone of influence".
At the same time, talks between the USSR, Britain and France over a co-ordinated response in the event of an attack by Nazi Germany, floundered.
Britain and France would not acquiesce to a key Soviet demand, namely that Soviet troops be allowed free passage across Poland.
One of the most enduringly controversial aspects of the pact was the Soviet policy to deny the existence of the secret protocol.
The secret protocol was signed by von Ribbentrop and Molotov
The policy built on Stalin's written rejection of claims relating to Soviet-Nazi co-operation, published in 1948 and known as The Falsifiers of History.
It was only in the late 1980s, the era of Mikhail Gorbachev's perestroika reforms, that the Soviet government admitted the truth.
The West never accepted - and viewed as illegal - the incorporation of the Baltic states into the Soviet Union.
Certainly, many people from the Baltic states made their own feelings clear when, on 23 August 1989, more than two million of them linked hands along the entire length of their countries' eastern borders to mark the 50th anniversary of the signing of the pact.
The leading British historian, Orlando Figes, described the pact as "a constant thorn in Russia's relations with neighbouring European states".
He suggested it continued to underpin the perspective in those states of post-war Soviet oppression.
The respected Polish-Belgian author Leopold Unger referred to the pact as the "most cynical operation of the World War II, and the founding document of the post-war Soviet empire in Europe".
Russian state archives do not allow historians unfettered access to the documents detailing Nazi-Soviet co-operation.
In early August, Russia's normally secretive SVR (foreign intelligence service) issued a rare statement asserting that the USSR had "had no other option than to sign" the pact.
The ultimate blame, it claimed, lay with Britain and France, for scuppering the tripartite negotiations in the summer of 1939.
This statement came just weeks after the Russian defence ministry published an essay by a high-ranking official, in which it was suggested that Poland was ultimately responsible for World War II, by refusing to acquiesce to "legitimate" Nazi territorial demands.
Does the appearance of such views suggest that a revisionist analysis of the pact is becoming widespread in the Russian establishment?
Russia now says Stalin had "no option" but to sign the pact
And is this linked to current, apparently official, efforts to rehabilitate Stalin as a "great statesman" - even if his victims are also recognised?
Alexander Dyukov, a young Russian historian who claims Soviet repression has been systematically exaggerated, wrote: "Attempts to compare or equate Hitler's regime with the USSR destroy the single historical focal point - our victory in the war - that holds together our society."
Mark Solonin, a liberal historian, takes a very different view.
"In one short act, Stalin threw Europe into mayhem, and abandoned the Franco-British bloc, whose leaders had already promised Poland security guarantees, to the maniac in Berlin," he wrote.
"After the signing of the pact, he fell into a state that can only be described as foolhardy bravery.
"A European war became unavoidable. It began precisely one week after the signing of the pact."
Russia increasingly maintains that the pact was a strategic document, driven primarily by considerations of self-defence.
It strongly rejects the idea that Soviet collusion with the Third Reich was a factor in the destruction of Europe that soon ensued.