The Cham people and their long history in Southeast Asia are a focus in this feature in National Geographic.

The Cham: Descendants of Ancient Rulers of South China Sea Watch Maritime Dispute From Sidelines
National Geographic, 16 June 2014
For centuries the South China Sea was known by navigators throughout Asia as the Champa Sea, named for a great empire that controlled all of central Vietnam, from the northern border of today’s Quang Binh Province to roughly the southern border of Binh Thuan Province.
At the peak of the Champa empire, from around the 6th to the 15th centuries, its various kingdoms, presided over by regional royal families, also included sizable portions of eastern Cambodia and Laos.
The oldest artifacts of a distinctly Cham civilization—brick flooring, sandstone pillars, and pottery found at Tra Kieu in Quang Nam Province—date to the second century A.D.
A notable Champa legacy is the red-brick temples, or Cham towers, the oldest found dating to the seventh and eighth centuries. The temple city of My Son, near Hoi An, preserved as a UNESCO World Heritage site, has nearly 70 individual structures.
Full story here.