I think I understand your discontent, and I’m not here to be bias towards any ethnicity or country.
From the very beginning, the Tai speaking people (Ancestors of the Thai, Lao, Shan, Tai Lu, Tai Dam, Tai Khum, etc. etc.) were all from the relatives of the Nanzhao Kingdom of the Yunnan province.
After the fall of the kingdom to the Chinese Dynasty, many would migrate southward and become apart of the Khmer Kingdom. They essentially adopted into Khmer & Pali Indian cultural influences. The Thai went south, and the Lao went east. Of course, the Khmer and the Chams were rivals, rivaling one another. The Khmer Empire would of course be successful, and thus creating the Angkor Wat from 800-1400’s.
However, like all empires, declines. The Lan Xang Kingdom of the Lao, the Ayuthaya, Lanna, etc. would eventually grow to become prosperous in the 1300’s-1700’s.
Then of course, the Thai and Burmese rivalry, the Thai would eventually conquer parts of Burma, Laos, Cambodia, Vietnam and Malaysia to become “Siam” in the 1700’s, until European reclaimed them back.
In my opinion, I think that it’s a shared history of Indochina.
Remember that it was the Khmer/Cambodians who gave the cultural brilliance to the Ancient Tai speaking people (Thai, Lao, Tai people, etc.) and the Burmese. It would be unfortunate that the Thai would be the last rulers of the once ago established Khmer Empire in the 1700’s, until the Europeans reclaimed the partial lands back from the Siamese.
But you have to understand that it was the Nationalism of the 1950’s~, and the effects of it today, when Thailand banned all non-Thai culture, language and writing, to assimilate others to essentially become Thai and boasted that “Thai people” are the best in Indochina, despite their adopted mother is Cambodian and their sister is Laotian. This has caused the Isan region of both Lao & Cambodians to switch their writings into Thai, the Tai Lu of the formal Lanna Kingdom of Northern Thailand to adopt to Thai writing styles, etc. etc.
I am very aware about the Nationalism that is going on in Thailand, and the conflicts between Thailand and Cambodia. So, it is wrong for some people to claim that “Angkor Wat” or that “Thai culture” is better than any others, particularly against Cambodian, Burmese and Lao culture, when the birth of those civilizations was thanks to the ancient Khmer Empire.
As someone of Cambodian background, first of all our culture is neither better not worse than anyone else’s culture. Especially to our neighbours, the Thais, Laotians and the Vietnamese.
What has happened has happened, and holding onto the past will keep our country in the past and prevent us from growing and being merely a tiny country.
Take a step into Thailand and Vietnam and mention that you are Khmer, and they will shrug their shoulders. They do not care about taking our land anymore. Worry about our growth as Cambodians. We have bigger issues to worry about than historically nationalistic dilemmas.