Complex sentence: Jackson became one of the most influential gospel singers in the world, and was heralded internationally as a singer and civil rights activist; entertainer Harry Belafonte called her "the single most powerful black woman in the United States".
Split into simpler sentences: Jackson became one of the most influential gospel singers in the world and was heralded internationally as a singer and civil rights activist. She was described by entertainer Harry Belafonte as "the single most powerful black woman in the United States".