Complex sentence: During the 1940s and 1950s, South Gate was one of the most fiercely segregationist cities in Southern California; gangs of white youths were known to prowl the streets looking for blacks who dared to cross over from neighboring Watts.
Split into simpler sentences: During the 1940s and 1950s, South Gate was one of the most fiercely segregationist cities in Southern California. Gangs of white youths were known to prowl the streets looking for blacks who dared to cross over from neighboring Watts.