Complex sentence: After the war of 1548, Maha Chakkraphat insisted on battling Burmese armies near Ayutthaya, so he heavily fortified the city and de-fortified three nearby cities, Suphanburi, Lopburi and Nakhon Nayok in order to prevent the Burmese from taking them as bases.
Split into simpler sentences: After the war of 1548, Maha Chakkraphat insisted on battling Burmese armies near Ayutthaya, so he heavily fortified the city. He, however, de-fortified other cities in order to prevent the Burmese from taking them as bases.