There are a few centers that specialize in Southeast Asia in the US - Cornell, Berkeley (my academic affiliation right now), Wisconsin, Yale, Michigan, Washington, Northern Illinois. When I was at Princeton (before Firaxis), I was one of two -
two - specialists in the region in the entire school. It was me, and a historian of the Indian Ocean who spoke Indonesian.
A lot of these institutes were set up with money in the 1960s for that exact reason that
@Boris Gudenuf mentions - Vietnam, and so Southeast Asian studies in the US became a political science focused discipline, unlike in, say, Germany, where it has more of a culture/literature feel. This includes the Philippines, by the way! Yes, they were an American colony for a time, but that didn't translate into sufficient academic focus. In many history departments, the region was ignored, largely because access to languages was difficult to find (meaning, too, that many historians of that era only read French, or Dutch). My own discipline, anthropology, was a little better, as the region did produce good scholarship (Geertz, Leach, Siegel, Steedly - including New Guinea, there was much more).
There are now fantastic historians and anthropologists working on the region - Vincent Rafael, for instance, on the Philippines is great; Ann Stoler, etc. Liam Kelley, the author of that post, is a good one, too. Now, too, there are great historians who are also from that region (Thongchai, Rafael, Hierianto, Thak). And Japanese scholarship on the region is good, too (Tanabe, Iishi). But for outsiders (raises hand), access to language training is hard to find, and the languages themselves can be hard.
Wolters - the father of the Srivijaya hypothesis - was great, and his model of "mandala state" is one I love. And one reason why I put that name as one of the name for a policy card.
But history is hard. Chinese and Roman ancient history has long, long records (Vietnamese, too, of course); Khmer and Majapahit less so, and Sukhothai, "Srivijaya," Champa, etc., have very, very little. Records left by travelers (Zhou Daguan, Ibn Battuta) can be vague ("I travelled to an island with a queen..." in Battuta gets appliedto Java, Champa, and the Philippines - Zhou, I should say, is far more detailed, even giving a little TMI on his own personal habits). We have to speculate based on what we have, and Srivijaya (and Sukhothai) become myths that fit too much what people want to see. For scholars of Southeast Asian history as with Southeast Asian states themselves, the desire to have a vast, forgotten empire is a strong one. On one hand, I'm happy to see the region get recognized by Amplitude (or us!), on the other hand what you see on Wikipedia or elsewhere often paints a picture that seems more clear than it really was.
Really spurious links get made, especially in the 60s and before. A reference in Chinese chronicles to "Ai-Lao" in Yunnan gets turned into a great Lao (Tai) empire (possible, but unlikely). An American missionary hears that the word for "Big" in some readings of Chinese is "Dai" and speculates that the word comes from a meeting between Chinese and Thai people (absolute bull****). Others are up for debate. Was Ramkhamhaeng real (in some form)? Was Sukhothai real (yes, but not to the extent that is claimed)? Were the Tasaday real (probably)? Was Srivijaya real (probably not)? And sticking a border around something and putting it in "your" civ puts a false binary onto the world. The Siamese at one point sent tribute to the Ming - does that make them part of the Empire? The Cambodians sent tribute to the Siamese AND the Vietnamese at the same time - where to put them? Lanna, Nan, Vientiane, Luang Prabang - these were all sometimes independent and sometimes vassals. To claim that "X empire = the total of everyone that ever sent tribute to its ruler" simply doesn't hold up.
Again, I quibble with the inclusion of Srivijaya, like I quibble with the inclusion of Sukhothai in Civ (and pushed for Ayutthaya instead in Civ6 as a city-state). Also, I note that their Khmer unit names are in Sanskrit, not ancient Khmer (roughly as if a Norman knight was called
eques or something - not
wrong in the sense that I'm sure people wrote about knights in Latin in Norman England, but not
right either). But I see that word, Srivijaya, and my eyes do light up -
someone is paying attention to this region!!