After Germany started its invasion of the Soviet Union on 22 June 1941 , the Soviet Union joined the Allies and signed an Anglo-Soviet Agreement on 12 July 1941 . This put the Polish Government in a difficult position , since it had previously pursued a policy of " two enemies " . Though a Polish-Soviet agreement was signed in August 1941 , cooperation continued to be difficult and deteriorated further after 1943 when Nazi Germany publicized the Katyn massacre of 1940
Katyn massacre
Katyn massacre
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