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 Yalta Conference (4–11 February 1945), the two crucial events in which the Western Allies and the Soviet Union discussed the shape of the post-war world and decided on the fate of Poland, assigning it to the Soviet sphere of influence. In Teheran, neither Churchill nor Roosevelt objected to Stalin's suggestion that the Polish government in exile in London was not representing Polish interests; as historian Anita Prażmowska noted, "this spelled the end of that government's tenuous influence and raison d'être." After the Teheran Conference, Stalin decided to create his own puppet government for Poland, and the PKWN was proclaimed in 1944. PKWN was recognized by the Soviet Government as the only legitimate authority in Poland, while Mikołajczyk's Government in London, was termed by the Soviets an "illegal and self-styled authority." Mikołajczyk would serve in the Prime Minister's role until 24 November 1944, when, realizing the increasing powerlessness of the government in exile, he resigned and was succeeded by Tomasz Arciszewski, "whose obscurity", in the words of historian Mieczysław B. Biskupski, "signaled the arrival of the government in exile at total inconsequentiality."