The wars which are now drawing to a close can be compared to the Thirty Years War (1618–48), the War of the Spanish Succession, which really began in 1688 and lasted until 1713, and the French Revolutionary and Napoleonic Wars (1789–1815). Each of these wars lasted thirty years or slightly less, and if we begin the present war in 1914, it already has become a fourth thirty-years war.

All of these wars left problems which had aspects in common. In all, there was the problem of returning to the ways of peace, of settling boundaries and governments, of reconstruction, and of maintaining a stable international order. But in each successive war the area involved was larger, the number of participants in the peace was greater, their economic relationships were more pervasive, and a more intensive international political organization was attempted.

At Westphalia in 1648, the effort was rather to establish the independence of states than to organize their interdependence. The ancient structure of the Holy Roman Empire and the universal spiritual authority of the Papacy were crumbling. The national independence of Switzerland and of the Netherlands and the virtual independence of the states of Germany were recognized. The notion of the sovereign territorial state, so different from the conception of a feudal hierarchy which had dominated medieval thinking, took root in men's minds and was promoted by the administration of efficient governments beginning to realize the possibilities of building power upon national sentiment.