Complex sentence: He accompanied Sir Thomas Fairfax in his expedition into Cheshire, commanded a brigade at the battle of Selby, and on the surrender of the castle of Sheffield was appointed governor of that place (August 1644), and a little later military governor of York.
Split into simpler sentences: He accompanied Sir Thomas Fairfax in his expedition into Cheshire, commanded a brigade at the battle of Selby. Briefly, he was appointed governor of that place (August 1644), and a little later promoted as military governor of York.