One thing that's telling is the when western / European explorers found ancient ruins in Southeast Asia, they assumed other Europeans had to have built them. Racism does it again, folks!

I would like to recommend the Fall of Civilizations podcast. There isn't an ep about Vietnam (or their predecesors), but their is a good ep about the Khmer Empire (now Cambodia). It's a great show all around. Has a YouTube channel, too, if you're into that. I'm fine with just audio and like letting my imagination entertain me.