Official propaganda exists in every country: you don't see Britain or France of Poland taking blame for letting Hitler run amok in Europe, do you? It's always the "Commies".
Just a quick historical recap of what was happening prior to the September the 1st, 1939.
After Hitler comes to power and starts hidden re-militarization of the Germany, Britain, France and Poland do nothing, silently looking how American and Sweden companies are building guns and ships for the Germany.
In 1938 Hitler demands control of the Sudetenland(part of Czechoslovakia). USSR starts negotiations with Britain, France and Poland willing to use army to protect Czechoslovakia. Poland refuses to let Soviet troops through its territory. Negotiations are artificially prolonged by Britain. Munich agreement is signed by the Britain, France and Germany, and Hitler gets a nice gift in a form of Czechoslovakia (you never see Britain and France talking about this, do you?).
On the 1st of September, 1939, Hitler invades Poland (Britain and France did not help their 'ally' in the slightest). USSR invades Poland 16 days later, when Poland ceased to exist as a sovereign state.
There were two pragmatic choices for the USSR: let Germany capture all the Poland and have their border be right at the gate, or prepare for the inevitable war with the Germany by capturing additional territory. No one in the USSR believed that Hitler will be a nice neighbor - there were a lot of information available on the Germany's descent into Nazism.
There is a similar story with Finland: USSR wanted to move their border further from the Leningrad (it was ~10-20 kilometers), because Leningrad is a major industrial center. USSR pragmatically wanted to trade territory with Finland, giving them a lot of land in exchange for that border shift. Finland refused. USSR was left with two choices: leave the border near your second largest city for an inevitable war (Finland was pro-Nazi) or solve this problem while Hitler is busy with France.
Just a quick historical recap of what was happening prior to the September the 1st, 1939.
After Hitler comes to power and starts hidden re-militarization of the Germany, Britain, France and Poland do nothing, silently looking how American and Sweden companies are building guns and ships for the Germany.
In 1938 Hitler demands control of the Sudetenland(part of Czechoslovakia). USSR starts negotiations with Britain, France and Poland willing to use army to protect Czechoslovakia. Poland refuses to let Soviet troops through its territory. Negotiations are artificially prolonged by Britain. Munich agreement is signed by the Britain, France and Germany, and Hitler gets a nice gift in a form of Czechoslovakia (you never see Britain and France talking about this, do you?).
On the 1st of September, 1939, Hitler invades Poland (Britain and France did not help their 'ally' in the slightest). USSR invades Poland 16 days later, when Poland ceased to exist as a sovereign state.
There were two pragmatic choices for the USSR: let Germany capture all the Poland and have their border be right at the gate, or prepare for the inevitable war with the Germany by capturing additional territory. No one in the USSR believed that Hitler will be a nice neighbor - there were a lot of information available on the Germany's descent into Nazism.
There is a similar story with Finland: USSR wanted to move their border further from the Leningrad (it was ~10-20 kilometers), because Leningrad is a major industrial center. USSR pragmatically wanted to trade territory with Finland, giving them a lot of land in exchange for that border shift. Finland refused. USSR was left with two choices: leave the border near your second largest city for an inevitable war (Finland was pro-Nazi) or solve this problem while Hitler is busy with France.