Complex sentence: Following his father's death in 1739, Isaac Jr. became noted as a slaveowner in Massachusetts over the subsequent decades-in 1754 he owned 12 enslaved Africans-six times more than any other household.
Split into simpler sentences: Following his father's death in 1739, Isaac Jr. became noted as a slaveowner in Massachusetts. In 1754, he owned 12 enslaved Africans, six times more than any other household.