Complex sentence: Phelps and Gorham defaulted on their payments to Massachusetts in 1790, and the pre-emption rights reverted to the state, which re-conveyed them to Samuel Ogden on behalf of Robert Morris on May 12,1791.
Split into simpler sentences: Phelps and Gorham defaulted on their payments to Massachusetts in 1790, causing the pre-emption rights to return to the state. Massachusetts then conveyed the pre-emption rights to Samuel Ogden on behalf of Robert Morris on May 12,1791.