George Gershwin visited African-American churches and nightclubs in South Carolina to craft the music for “Porgy & Bess.” Years after his death, the opera and its all-star cast played an unexpected role in Cold War relations.

Making music under Stalin was a dangerous undertaking — it could end with applause or in a prison camp. In the brutal grip of World War II, Shostakovich composed a symphony so powerful, it was smuggled halfway around the world in order to be played.