During the Second World War , Sikorski became Prime Minister of the Polish government-in-exile , Commander-in-Chief of the Polish Armed Forces , and a vigorous advocate of the Polish cause in the diplomatic sphere . He supported the reestablishment of diplomatic relations between Poland and the Soviet Union , which had been severed after the Soviet pact with Germany and the 1939 invasion of Poland — however , Soviet leader Joseph Stalin broke off Soviet-Polish diplomatic relations in April 1943 following Sikorski 's request that the International Red Cross investigate the Katyń Forest massacre
Katyń Forest massacre
Katyn massacre
Władysław Sikorski