What are the motifs in The Mask of Command by John Keegan?

Military training and command is a recurring idea. Although the leaders covered in the book have as many differences as similarities, the one thing they all have in common was the duty of being a commander of one or more armies. Each may have had a different approach to the way troops and warfare should be treated and conquered, but it is clear that each man had a definite vision and the fortitude to carry it through.