Complex sentence: The ruler of Travancore, Marthanda Varma, routed an invading Dutch fleet; the Dutch commander, Delannoy, joined the Travancore army and served for decades; the Dutch never recovered from this debacle and were never again a colonial threat to India.
Split into simpler sentences: The ruler of Travancore, Marthanda Varma, routed an invading Dutch fleet. The Dutch did not recovered from the debacle and were never again a colonial threat to India.