A wonderful example of long-persistent delusion was the Crusades. For nearly two centuries (1095–1289) the Christian nations of Europe neglected state and domestic affairs in order to rescue the Holy Sepulchre from the hands of the infidels. All classes, from kings to peasants, fell a prey to the same obsession. It was accompanied by repeated and unmistakable signs of epidemic manias and neuropathias unequalled in history. Lykanthropy, in which the possessed howled and destroyed like wolves, was extremely common; the dancing mania spread through wide areas, forcing old and young into wild gestures and crazy motions; and, stranger than all, young children were attacked with a mad desire to leave their homes and to wander forth they knew not whither. Were they prevented, they pined and died. These “children’s crusades” began in Germany in 1212, extended through France, Switzerland, and Italy, and continued as late as 1418.
_(b) Dominant Ideas._—The weightiest topic in universal history may possibly be the study of dominant or fixed ideas in ethnic psychology. A philosophic observer may regard each nation as the destined representative of some one idea, which, when its usefulness has ended, yields to others more germane to existing conditions; and by the successive action of all, the progress of the species is secured through the gradual elimination of those which are regressive.
Certain it is that in any group the constituent minds are controlled at a given time by some one idea common to all. This is, in one sense, a perversion of the intellect. The dominant idea assumes a magnitude out of proportion to its actual value; and by this disproportion—that is, by the undue attention it receives, others, often of equal or greater value to the group, are neglected.
These dominant ideas form the national ideals, after which the individual lines are consciously patterned, and by the practical application thus given, add to the cohesion of the group through the unification of its members. Acting under natural laws, common to organic forms as well as to societies, these ideas are the chief agents in social selection, and thus control almost absolutely the traits and destinies of nations, as has been traced in a masterly manner by Vacher de Lapouge.