One of four new ""Portraits of the Nations,"" by the author of excellent books on China (1989) and Mongolia (1990) in the series, this is a typically thorough, comprehensive survey of the geography, history, and culture of a land with several competing ethnic groups. Major clearly portrays the aspects and origins of cultural diversity and the resulting challenges the two governments here face. (Brunei, a small sultanate, ""declined to join"" when the country of Malaysia was formed in 1963.) The author's tone is rigorously objective except in a chapter on ""Daily Life,"" where fictionalized portraits of members of various cultural groups dramatize their differences. Elsewhere, the style is dry, even encyclopedic, more appropriate for consultation than for lengthy perusal. Still, a fine resource, the most complete on its subject for young readers. Many rather dark but well-captioned b&w photos; boxed ""minifacts""; maps; tables; annotated chapter-by-chapter bibliography; index.