The similar sides of Communism and National Socialism... Both were police states both carried out similar crimes against there own people and others.. Both were Darwinistic in there goals.

Valentine McEntee in the House of Commons on the 20 October 1939:
... Had it not been for the pact between Russia and Germany, had Russia stood aloof from the pact, it is very doubtful whether Germany would ever have taken the step that she did take of sending troops into Poland.
http://www.electronicmuseum.ca/Poland-WW2/nazi_soviet_friendship/nsf_relations.html

. In the first period of Soviet-German friendship from 1939 to the middle of 1941, no detail of these negotiations was disclosed. The different white, yellow and blue books, published by governments in 1939 display no knowledge of them. It was not known that Molotov and von Ribbentrop signed not only an open, but also a secret agreement in Moscow on the 23 August 1939.
2. Even after the outbreak of the Soviet-German war on the 22 June 1941, and until the end of war in 1945, both parties continued carefully to conceal their previous agreements, displaying a most striking similarity in their attitude in this respect. In his speech, made on the very day of the attack on Russia, Hitler limited himself to a most general and very veiled mention of an annex to the open agreement of the 23 August 1939:... A special agreement was concluded in case Britain should succeed in inciting Poland actually to go to war against Germany, and in this case, too, the German plans were subject to a limitation entirely out of proportion to the achievements of the German forces.Thus Hitler reproached Russia for having secured too high a price. Moscow turned a deaf ear.
3. After the war, in 1945, when the British and Americans occupying Western Germany took possession of the archives of the German ministry of foreign affairs [Auswärtiges Amt], up to the end of 1946 their behaviour was different from their actions after the beginning of 1947. In the first stage, the German documents were used for the Nuremberg Trial in 1946, but nothing was disclosed that might have been considered to put the blame on Russia. But at nearly the same time, as Pres. Truman made his famous speech of the 12 March 1947, Prof. Harold C. Deutsch, who was officially entrusted with the research into the German archives, published in the Evening Star [March 10-13] in Washington a four-installment essay on Soviet-German friendship from 1939 to 1941, and at the beginning of 1948 the US State Department published the complete collection of documents, entitled NAZI-SOVIET RELATIONS, 1939-1941.