Complex sentence: Colonel Robert Lilburne (1613--1665) was the older brother of John Lilburne, the well known Leveller, but unlike his brother who severed his relationship with Oliver Cromwell, Robert Lilburne remained in the army.
Split into simpler sentences: Colonel Robert Lilburne (1613--1665) was the older brother of John Lilburne, the well known Leveller. Unlike his brother, who severed his relationship with Oliver Cromwell, Robert Lilburne remained in the army.