Winterbottom is old-school British military: dutiful, patriotic, and obedient to commands from his superiors, even when he disagrees with their orders. At first, we assume Winterbottom simply likes his powerful position when he brags about his reputation in Umuaro. But soon we discover that Winterbottom really believes in the African projects. And not only that, but he holds himself to very high moral standards because he wants to be an example to the Africans around him.
We can see that the Administration's inflexibility and lack of respect for experienced men like Winterbottom who have lived in Africa for years eats away at him. In the final scene, Winterbottom expresses total contempt for the orders of his superior.