Complex sentence: The peace was short-lived, and Henry invaded the Duchy of Normandy in 1105 and 1106, finally defeating Robert at the Battle of Tinchebray; he kept Robert imprisoned for the rest of his life.
Split into simpler sentences: The peace was short-lived, and Henry invaded the Duchy of Normandy in 1105 and 1106, finally defeating Robert at the Battle of Tinchebray. Henry kept Robert imprisoned for the rest of his life.