Complex sentence: He imprisoned Asim for embezzling money and failing to campaign against the rebels, and immediately took the field himself, and soon gained the upper hand in a succession of victorious, if costly, battles with Harith's supporters.
Split into simpler sentences: He imprisoned Asim for embezzling money and failing to campaign against the rebels, and immediately took the field himself. He soon gained the upper hand in a succession of victorious, if costly, battles with Harith's supporters.