Seeing as we live in Vietnam, here is a little historical piece I just researched and wrote up:
The Fall of the Champa
The Chams once ruled a Hindu influenced kingdom called Champa (Chăm Pa) whose rule extended through what is now central and southern Vietnam and parts of Cambodia. Cham society was organised in a cluster of city-states, not very different from ancient Greece. They were quite advanced with walled cities, palaces, monuments, books and archives, many of which were built by slaves. It had a powerful fleet that was used for commerce with China, India, the Indonesian islands, and the Middle East. A lot of the shipping trade came out of the Cham city of Lâm Ấp Phố (present day Hội An) which was the largest harbour in South East Asia in the 1st century. Due to lack of arable land in their narrow territory, they also resorted to piracy all along the present coast of Vietnam. Champa had a history of constant conflict with the Dai Viet (Vietnamese), Khmer (Cambodians), Java (Indonesians) and later the Mongols.
The downfall of Champa occurred in 1471 when the Vietnamese Emperor, Lê Thánh Tông, an extraordinary administrator and leader, invaded Champa with a huge force outnumbering the Cham by three to one. The Vietnamese army was well organised and had large numbers of gunpowder weapons, an idea modeled on the Chinese army of the time. By contrast the Cham were without any gunpowder weapons.
The Vietnamese army killed 60,000 when taking and destroying the capital Vijaya, and then they proceeded to burn massive parts of Champa, soon seizing most of the country. The Vietnamese took 30,000 Cham as slaves and enacted forced assimilation of Vietnamese culture onto the Cham people.
After that time, Cham dissidents to the absorption were forced into exile or scattered to remote villages in the mountains. The majority migrated Cambodia and others to Malaysia and Thailand where they remain to this day.