Here are the completed sentences with the correct forms of the provided words:

1. Vietnam is one of the most **ethnic** diverse countries in Southeast Asia.
2. The Pa Then believe that the god of fire brings them **peace** and prosperity.
3. The Tay community practice **traditional** religious beliefs including ancestor worship.
4. The population of Vietnam contains a rich **diversity** of ethnic groups.
5. Each time I returned I was struck by the **uniqueness** of Sapa and its people.