The evolution of international relations dominates the entire history of the period between the Peace of Westphalia (1648) and the Treaties of the Pyrenees (1659) and of Oliva (1660). These few years saw the termination of the Thirty Years War, of the war between France and Spain and of the war in the north. But, apart from some territorial adjustments arising from the Treaty of the Pyrenees, these conflicts appear to be of minor interest; they did not transform the map of Europe. The appearance is misleading, for this short period, when the first indications of French supremacy emerged to view, witnessed a change in the relations between the European powers. It saw the end of the Franco-Swedish axis which had dominated the history of the Thirty Years War, the final downfall of Spain and the decline of Sweden and Poland, the entrance of Russia into European politics and the rise to power of the little state of Brandenburg. Finally, with the first Anglo-Dutch War, came the confident assertion of English sea-power in an alliance—albeit episodic—with France. The shifting of power, the emergence of new forces or rather of new ambitions, the breakdown of the old European equilibrium which was everywhere in a state of collapse—these are the themes it is proposed to elucidate, taking as a guiding thread the policy of France which gives unity to the whole.

Although it brought peace in Europe, peace in Germany and a constitutional charter, the achievement of the Peace of Westphalia remained incomplete. It had provided a lasting solution to some of the problems from which it stemmed, notably to the religious question on the basis of a reciprocal tolerance between the Catholic, Lutheran and Calvinist faiths; it also assured the exercise of territorial sovereignty to princes and cities; finally, it gave the victorious states substantial 'satisfactions': yet it was, above all else, a 'potentiality', calling for careful surveillance by France if all its rewards were to be reaped.