Complex sentence: There were several pressures occurring in the colony which lead to greater restrictions on the slave trade, the greatest of which was the pressure applied by the Quakers, who comprised a large percentage of Rhode Island's population.
Split into simpler sentences: There were several pressures occurring in the colony which lead to greater restrictions on the slave trade. Probably the greatest of these was the influence of the Quakers, who comprised a large percentage of Rhode Island's population.