Complex sentence: Seeing them united in a cause alarmed the ruling class, historians believe the rebellion hastened the hardening of racial lines associated with slavery, as a way for planters and the colony to control some of the poor.
Split into simpler sentences: Seeing them united in a cause alarmed the ruling class. Historians believe the rebellion hastened the hardening of racial lines associated with slavery, as a way for planters and the colony to control some of the poor.