Complex sentence: Wasilewska, an informal leader of Polish communists, was received by Stalin at the Kremlin on 28 June 1940, which marked a beginning of reorientation of Soviet policies in respect to Poles, with momentous consequences for the next half-century.
Split into simpler sentences: Wasilewska, an informal leader of Polish communists, was received by Stalin at the Kremlin on 28 June 1940. The event marked a beginning of reorientation of Soviet policies with respect to Poles, which had momentous consequences for the next half-century.