Why were the kingdoms of Southeast Asia so tragic? This question deals with the time of the Gupta empire and Maurya empire.
Simply put, the kingdoms of Southeast Asia were so tragic because they were inhabited by races of people who were fierce and unyielding, often to the point of fanatism. Often considered barbarians by we Westerners, they had different ideals when it came to honor, valor, social position, morals, and religious beliefs.
While the western world was learning about democracy and Christianity, with an emphasis on equality and getting along with their neighbor, the eastern world was (and to a great degree still is) deeply entrenched in feudalism and the caste system. These systems are based upon the premise that one person or set of persons are better than the rest and entitled to rule. Those less fortunate than themselves were nothing and didn't deserve anything. Although there were a few philosophers and rulers through the ages who were kind, looked out for others, and taught enlightened principles, for the most part, most were uncouth, undisciplined, and unkind. Unfortunately, it was these masses who perpetuated the traditions and practices that have gone on for centuries.
Please keep in mind that Southeast Asia today has many intelligent, cultured, refined, brilliant people! They have risen above their often dark, bloody past to be great people.