>>17768493 (OP)
idk about backstabbing but the thais were the most recent/youngest SEA civ. before that it was separate small kingdoms who doest really amount to anything excep getting periodically raped by Burmese empire from the east. Ayuthayya exploited the vacuum left after the burmese empire and played the french and brits off each other to survive while doing opportunistic land grabbing here and there.
