Complex sentence: He strikes a deal with the revolutionary army and does so mainly in his own self-interest and protection but being the own of such a large swath of land he is, by extension, in charge of the physical well-being of the town.
Split into simpler sentences: He strikes a deal with the revolutionary army and does so mainly in his own self-interest and protection. But being the owner of such a large swath of land, he is, by extension, in charge of the physical well-being of the town.