Wars of conquest were less frequent in the Middle Ages
than we might expect, and were usually waged on a small scale. Their
comparative infrequency, in an age of militarism, must be explained by
reference both to current morality and to economic conditions. For an attack
upon a Christian power it was necessary that some just cause should be alleged.
Public opinion, educated by the Church to regard Western Christendom as a
single commonwealth, demanded that some respect should be shown to the ordinary
moral code, even in international relations.
Furthermore the medieval state,
loosely knit together and bristling with isolated fortresses, showed in defeat
the tenacious vitality of the lower organisms, and could not be entirely
reduced without an expenditure, on the invader's part, which the methods of
medieval state-finance were powerless to meet. Edward I failed to conquer the petty
kingdom of Scotland; and the French provinces which were ceded to Edward III
escaped from his grasp in a few years. The profitable wars were border wars,
waged against the disunited tribes of Eastern Europe, or the decadent Moslem
states of the Mediterranean. And such wars were of common occurrence, sometimes
undertaken by the nationalities most favourably situated for the purpose,
sometimes by self-expatriated emigrants in search of a new home.
