The fighting between Ayutthaya and Lan Na resumed between 1494 and 1530. During this period, Lan Na constantly raided their neighbors to their south while Ayutthaya repeatedly mounted invasions in retaliation. Ramathibodi II became king of Ayutthaya in 1491 and ruled until 1529. He instituted compulsory military service to help fight his wars. The Burmese-Siamese War in 1547-49 was inconclusive. A much more dangerous threat developed when Bayinnaung became king of Burma in 1551. Starting in 1563 Bayinnaung conquered both Lan Na and Ayutthaya. The Burmese were not ejected until the Thai revolt of 1587.. How many years did The Burmese-Siamese War last?