After Germany started its invasion of the Soviet Union on 22 June 1941, the Soviet Union joined the Allies and signed the 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". Although a Polish–Soviet agreement was signed in August 1941, cooperation continued to be difficult and deteriorated further after 1943 when Nazi Germany publicised the Katyn massacre of 1940.