Why did slave rebellions and the fear of slave revolts consume the attention of white colonists in the south and the north in the 1730s and the 1740s?

Slave rebellions and the fear of slave revolts consumed the attention of white colonists in the south and the north in the 1730s and the 1740s because the ratio of slaves to whites was often very high--meaning that the only thing keeping such revolts from taking place more often was fear and violent intimidation.