Complex sentence: Under contract from the Louisiana Purchase Exposition, Verner negotiated Benga's release from slave traders in 1904 following his capture by the Force Publique--which had also attacked his village, killing Benga's wife and two children.
Split into simpler sentences: Under contract from the Louisiana Purchase Exposition, Verner negotiated Benga's release from slave traders in 1904. He had been captured by the Force Publique, which had attacked his village, killing Benga's wife and two children.