Complex sentence: Sayle himself went on to become Governor of South Carolina, but continued to have a vested personal interest in Eleuthera and used his influence as Governor of South Carolina to secure some trade for the island and so helped it through its infancy.
Split into simpler sentences: Sayle himself went on to become Governor of South Carolina, but continued to have a vested personal interest in Eleuthera. He used this influence to secure some trade for the island and so helped the community through its infancy.