 Complete the following phrase:  Events taking place in 1943 significantly weakened the Polish government in exile. A rift developed between Poland and the Soviet Union, an increasingly important ally for the West, particularly after the revelation of the Katyn massacre in 1943 on 13 April, followed by the breaking-off of diplomatic relations with Poland by the Soviets on 21 April. The subsequent death on 4 July of the charismatic General Sikorski, succeeded by less influential Stanisław Mikołajczyk as the Prime Minister, and General Sosnkowski as the Commander-in-Chief, contributed to the decline. No representative of the Polish government was invited to the Tehran Conference 28 November  1 December 1943 or the 