Complex sentence: Yi I returned in the early 1580s (Jeong Cheol also returned), and in 1582 declared himself a Westerner, revoking his earlier position as a neutral observer.
Split into simpler sentences: Yi I returned in the early 1580s, as well as Jeong Cheol. In 1582, Yi declared himself a Westerner, revoking his earlier position as a neutral observer.