Generally speaking, the Middle Ages accepted war with fatalism. It was part of the divine plan, linked with famine, flood, and plague as a manifestation of God's punishment for sins committed. A nation which experienced years of defeat and disaster (as France did in the mid-fourteenth century) beat its breast in self-reproach and accepted war's afflictions. Since few questioned such a view, those of pacific leanings met with little sympathy. While war's excesses were often condemned, war itself was taken for granted. In a society whose social and economic system had originally been, and to a certain degree still was, organised to provide for such eventualities, this was scarcely surprising. A world geared to war was unlikely to question why it should break out. It formed part of the accustomed and natural order.

In more questioning times, with the historian seeking to exercise his right to examine the past, people have tried to explain why wars occur. Attempts to do this are far from new. Long ago, Thucydides distinguished between causes and occasions of war. In modern times, people have looked to many different aspects of human activity as sources of conflict, not all of which may be seen as appropriate to medieval societies. But some are. The Crusades may be regarded as wars fought in the name of ideology and religion. The Italian city states, and others, were for centuries in conflict in the Mediterranean over sources of, and outlets for, trade.