Complex sentence: On April 17,1944, Pravda ran a lengthy feature on the commemoration of Griboyedov's 150th birthday when high-ranking officials, military leaders, diplomats, writers, and artists had attended a celebration in the Bolshoi Theatre.
Split into simpler sentences: On April 17,1944, Pravda ran a lengthy feature on the commemoration of Griboyedov's 150th birthday. Many highly ranked officials, military leaders, members of the diplomatic corps, writers, and artists, had attended a celebration held in the Bolshoi Theatre.