Complex sentence: The cigar industry was the most important in Tampa's economy at the time, and was especially important in Ybor City, where a high percentage of residents were employed either in the cigar factories or in businesses catering to the cigar industry or its employees.
Split into simpler sentences: The cigar industry was the most important in Tampa's economy at the time. It was especially important in Ybor City, where a high percentage of residents were employed either in a cigar factory or in a business serving the cigar industry and its employees.