Complex sentence: Conrad Weiser was able to negotiate one of the more successful, in which some lower-level chiefs deeded to the colony most of the land remaining in present-day Pennsylvania, including the southerwestern part, still claimed by Virginia.
Split into simpler sentences: Conrad Weiser was able to negotiate one of the more successful agreements. Some lower-level chiefs deeded to the colony most of the land remaining in present-day Pennsylvania, including the southwestern part still claimed by Virginia.