Complex sentence: Many white people regarded black people as a social and economic threat, and countered their presence with local zoning laws requiring them to live and reside in geographically defined areas of the town or city, preventing them from moving to areas inhabited by white people.
Split into simpler sentences: Many white people regarded black people as a social and economic threat, and countered their presence with local zoning laws. Such laws required them to live and reside in geographically defined areas of the town or city, preventing them from moving to areas inhabited by white people.