Complex sentence: After a series of defeats suffered by Mughal commanders and Sikh victories, Mirza Najaf Khan personally took the field he decisively defeated the Sikhs and their Rohilla ally Zabita Khan, in 1779.
Split into simpler sentences: After a series of defeats suffered by Mughal commanders and Sikh victories, Mirza Najaf Khan personally took the field. He decisively defeated them and their Rohilla ally Zabita Khan, in 1779.