With his rousingly entertaining directorial debut, Sidney Poitier helped rewrite the history of the western, bringing Black heroes to a genre in which they had always been sorely underrepresented. Combining boisterous buddy comedy with blistering, Black Power–era political fury, Poitier and a marvelously mischievous Harry Belafonte star as a tough and taciturn wagon master and an unscrupulous, pistol-packing “preacher,” who join forces in order...