I seek to present here a causal explanation of the Vietnam War and to probe its meaning for the modern historical experience. I will examine in considerable depth the Communist Party, the Republic of Vietnam, and the United States. By focusing on how each side was affected by larger military, economic, social, international, and political-ideological structural trends operating simultaneously, I am able to juxtapose forces and factors influencing the outcome of the war and to highlight decisive elements in it. - Preface.