Neither the internal development of the medieval state nor the international politics of medieval Europe can be explained without constant reference to class distinctions. First, there is a sharp line dividing each state horizontally and marking off the privileged few from the unprivileged many, the rulers from the ruled. Below the line are the traders, artisans, and cultivators of the soil; above it the landlords, the officeholders, and the clergy. If an industrial community, here and there a Milan or a Ghent, succeeds in asserting political independence, the phenomenon is regarded as anomalous and revolutionary; still graver is the head-shaking when mere peasants, like the Swiss, throw off what is called their natural allegiance. And such cases of successful rebellion are rare. It is true that in England, in France, and in the Spanish kingdoms there are privileged towns which receive the right of representation in national assemblies; but this concession to the power of the purse is strictly limited; the spokesmen of the burgesses are not invited to express opinions until asked for subsidies or military aid. Government is the affair of the King and the privileged classes. But again there is a division within the privileged classes, a vertical line of cleavage between the various grades of the lay and clerical aristocracies. The prelate and the baron, the knight and the priest, harmonious enough when it is a question of teaching the unprivileged their place, are rivals for social influence and political power, are committed to conflicting theories of life. The ecclesiastic, enrolled in an order which is recruited from every social grade, makes light of secular rank and titles; he claims precedence over every layman; he holds that it is the business of the Church to command, of princes to obey. The lay feudatory, born into a hereditary caste of soldiers, regards war as the highest vocation for a man of honour, is impatient of priestly arrogance, and believes in his heart that the Church ought not to meddle with politics. It would be a mistake to think of the two privileged classes as always at strife with one another and their social inferiors. But the great wars of Pope and Emperor, the fourteenth-century revolts of French and English peasants, are not events which come suddenly and unexpectedly; each such outbreak is like the eruption of a volcano, a symptom of subterranean forces continually in conflict. The state of peace in medieval society was a state of tension; equilibrium meant the unstable balance of centralising and centrifugal forces. And this was one reason why wars, condemned in the abstract by the Church, were frequently regarded with favour by sober statesmen and by idealists. In more ways than one a successful war might serve to heal or salve the feuds of rival classes. It offered an outlet for the restless and anarchic energies of feudalism; sometimes it ended in conquests with which the landless could be permanently endowed.