Scholars and military practitioners alike have long sought to understand why the militaries of some countries fight hard when facing defeat, while others collapse. Castillo presents a new unifying theory - cohesion theory to explain why national militaries differ in their staying power. His argument builds on insights from the literatures on group solidarity in general and military effectiveness in particular. Specifically, he argues that two types of ties determine the cohesion, and therefore the resilience, of a nation's armed forces during war : the degree of control a regime holds over its citizens and the amount of autonomy the armed forces possess to focus on training for warfighting.

Cohesion theory : explaining a military's will to fight -- Germany, 1944-1945 -- France, 1940 -- The Soviet Union, 1941 -- North Vietnam, 1965-1973 -- The United States, 1968-1972.