Because of poverty, he was unable to continue his research.
Literal
Poorness [because-of-のため] he [topic-は] research [object-を] continuing [could-not-ことが出来なかった].
貧しさ uses the nominalizing suffix さ to turn the i-adjective 貧しい into the abstract noun 'poorness/poverty.' ことが出来なかった is the formal potential negative, more formal than the simple potential 続けられなかった.