Complex sentence: Sometime in the 11th century Norman Lord Payn de Turberville approached Morgan to turn over control of the Coity Castle to de Turberville but only if he (de Turberville) either fought Morgan for the land, or took his daughter Sybil's hand in marriage.
Split into simpler sentences: Sometime in the 11th century Norman Lord Payn de Turberville approached Morgan to turn over control of Coity Castle to de Turberville. Morgan Gam agreed, but only if de Turberville either fought Morgan for the land, or took Gam's daughter Sybil's hand in marriage.