What is the author's style in Winston Churchill: A Penguin Life by John Keegan?

The perspective of Winston Churchill: A Penguin Life is exclusively that of its author, John Keegan. Born in 1934, Keegan grows up, as he makes clear, thinking of Churchill as a reactionary Conservative who, while a great wartime leader, makes a poor peacetime Prime Minister. He notes that his perspective on Churchill changes substantially when he comes to the United States and starts to appreciate the United States' people's admiration for him, particularly when he hears a record of Churchill's wartime speeches.