American Partisan has a brief but good article up, One Critical Thing Your Group May Be Missing. Esprit de corps can be viewed as a group’s commitment, loyalty and attachment to each other and to their organization’s mission. A group with high esprit de corps and high member morale inspires individual members to execute their duties and responsibilities beyond expectations, leading to success reaching and exceeding the group’s goals. Individuals with high morale give their best service to the group. Confidence in the group’s cause, organization, leadership, methods and direction all contribute to individual high morale and, thus, group esprit de corps.
[W]hether regular organized units, survival groups, or guerrilla partisans resisting “enemies foreign and domestic,” the morale of the unit is almost as important as the combined unit skill sets. A less skilled, equipped unit with a high standard of motivation and sense of purpose can achieve as much as a well equipped, well trained, low morale unit. Throughout history, smaller ill prepared forces with a collective motivating goal have successfully hindered overwhelmingly superior forces that had less than ideal morale.
According to Harvard sociologist Alexander H. Leighton, “Morale is the capacity of a group of people to pull together persistently and consistently in pursuit of a common purpose.”