What is the author's style in Crazy Horse and Custer: The Parallel Lives of Two American Warriors by Stephen E. Ambrose?

The author writes authoritatively on this subject. The author is noted to have specialized in this area. He was published for many decades in the area of political and military history.

Ambrose neatly organized the book into four main parts, including supplemental information at each end. The entire package is delivered neatly and with a clear order of progression. The presentation is chronological, which although not a requisite of biography, is not uncommon.