Religion played a tremendous role in the forms of government in Southeast Asia.
Hinduism and Buddhism primarily were factored into forms of government in Southeast Asia. This was because when introduced and spread to many different places, both religions introduced concepts and ideas that shaped how the country managed itself. One example of an idea brought to Southeast Asia would be that rulers and/or leaders were believed to have been “chosen” or have a close form of communication and association with deities.
The same can be said about areas influenced widely by Islam. In many Muslim-populated places, governments were established according to religious beliefs (Sharia, ummah, etc.).
Although many historical events led to the establishment and foundations of government, religion widely tied into a lot of factors leading up to the forms of government we have today.