For general background, from Strange Parallels by Victor Lieberman (who studies Myanmar), volume one:
In mainland Southeast Asia military technology and strategy were more conservative than in Sengoku Japan or early modern Europe, and perhaps early modern South Asia. With broad, inhospitable marches separating some of the chief potential antagonists, fewer opportunities arose for extended conflict. Whereas in Europe printing, mercenaries, and a common cultural subtext sped the latest techniques from the English Channel to the Urals, and whereas in Japan a relatively unified culture also encouraged a rapid sharing of military advances, in mainland Southeast Asia poor east–west communications and the Indic-Sinic divide prevented a comparable fluidity.Moreover, compared to Japan, Europe, or South Asia, populations were smaller and commercial economies more sluggish, which was critical insofar as: a) Southeast Asia lacked the financial and credit mechanisms to maintain large standing armies and b) the absence of large-scale indigenous gun manufacture reduced the pressure for changes in weapons production, training, and finance.