Between the years 1100 and 1500 A.D. the state-system of Europe passed through changes amounting in their sum-total to a revolution. But the changes which endured, whether they affected political boundaries or constitutions, came about by slow instalments. At no stage of the development was there any general cataclysm such as had followed the dissolution of the Frankish Empire, and was to follow the advent of Napoleon. New ideas matured slowly in the medieval mind; by the twelfth century the forces making for social stability had grown until they balanced those of disruption; and it was only in the age of the Renaissance that the equilibrium was again destroyed. In the interim the vested interests of property and privilege, of religious and secular authority, presented a firm front to the anarchists and radicals. The Jacquerie in France and Wat Tyler's followers in England, the Albigeois of Languedoc and the Hussites of Bohemia, were overwhelmed by armies of conservatives spontaneously banded together in defence of the established order; - while this spirit prevailed among the ruling classes, there was little fear that a revolution of any kind would be effected by a sudden stroke. As in domestic politics, so too in international relations, these solidly established states were habitually inert, strong in defence, but irresolute and sluggish in attack. The age produced no conqueror to sweep through Europe like a whirlwind, because the implements of conquest on the grand scale had either been destroyed or had not yet come into existence. The peoples of Europe had emerged from the nomadic stage of culture, and they were not yet organised as so many armed camps. The feudal host was hard to mobilise, harder still to keep in the field, and at the best an unmanageable weapon; a standing army of mercenary soldiers would have called for taxation heavier and more regular than any ruler dared to demand, or any people could afford to pay. The wars of the Middle Ages have therefore, with few exceptions, a stamp of futility and pettiness. Ambitious enterprises were foredoomed to failure, and powers apparently annihilated by an invading host recovered strength as soon as it had rolled away. In short, on the European and on the national stage alike, medieval politics meant the eternal recurrence of the same problems and disputes, the eternal repetition of the same palliatives and the same plan of campaign. It is true that political science made more progress than the art of war. But substantial reforms of institutions were effected only in a few exceptional communities - in Sicily under the Normans and Frederic II, in England under Henry II and Edward I, in France under Philip Augustus and his successors. Even in these cases the progress usually consists in elaborating some primitive expedient, in developing some accepted principal to the logical conclusion. The more audacious innovators, a Montfort, an Artevelde, a Frederic II, were tripped up and overthrown as soon as they stepped beyond the circle of conventional ideas. It will therefore suffice for our present purpose to state in the barest outline the leading events of international politics, and the chief advances in the theory of government, which signalised the Middle Ages.

Extensive diplomatic combinations, though continually planned, seldom came to the birth and very rarely led to any notable result. The existence of some common interests was recognised; no power viewed with indifference any movement threatening the existence of the Papacy, which represented religious unity, or of the crusading principalities which formed the outer bulwark of Western Christendom; the principle of the Balance of Power, though not yet crystallised into a dogma, was so far understood that the inordinate growth of any single power alarmed the rest, even though they stood in no imminent danger of absorption. Therefore whenever the Empire gained the upper hand over the Church, whenever a new horde of Asiatics appeared on the horizon, whenever France seemed about to become a province of England, or Italy a province of France, the alarm was sounded by the publicists, and there ensued a general interchange of views between the monarchies; treaty was piled on treaty, alliance parried with alliance, as industriously as at any time in modern history. But the peoples seldom moved, and the agitation of the ruling classes effervesced in words. It is altogether exceptional to find two of the greater states uniting for the humiliation of a third, as England and the Empire united against Philip Augustus of France. Few medieval battles were so far-reaching in their consequences as Bouvines (1214), to which England owes her Magna Carta, Germany the magnificent and stormy autumn of the Hohenstauffen dynasty, France the consolidation of her long-divided provinces under an absolutist monarchy.

At ordinary times there were in medieval Europe two groups of states with separate interests and types of polity. They were divided from one another by a broad belt of debatable territory, extending from Holland to the coast of Provence - the northern lands of the Carolingian Middle Kingdom.