Boston was an early port of the Atlantic triangular slave trade in the New England colonies, but was soon overtaken by Salem, Massachusetts and Newport, Rhode Island. Eventually Boston became a center of the abolitionist movement. The city reacted strongly to the Fugitive Slave Law of 1850, contributing to President Franklin Pierce's attempt to make an example of Boston after the Anthony Burns Fugitive Slave Case.
Boston was overtaken by Salem, Massachusetts in what type of trade? 
slave trade