Complex sentence: He engaged in bowyering as a sideline in the mid 1980s, then reconstructed the Hungarian composite bow from the conquest era, eventually this became his profession, and he became the first in the world to mass-produce this bow.
Split into simpler sentences: He engaged in bowyering as a sideline in the mid 1980s, and reconstructed the Hungarian composite bow from the time of the Hungarian Conquest. Eventually this became his profession, and he became the first in the world to mass-produce this bow.