What american argued that overseas expansion was a safety valve to keep ambitious americans content?

Why would southern delegates to the constitutional convention have opposed the three-fifths compromise? a) they feared that the president would eventually become "king" in the united states. b) they believed it would be insufficient in protecting the united states from invasion. c) they opposed the creation of a congress that would give states an equal number of senators. d) they wanted their full population of slaves to be counted for purposed of congressional representation.