"Almost any student who has read the usual books, if he were asked to mark what was the foremost idea of the three centuries that intervene between the year 1500 and the year 1800, would reply that it was the idea of the balance of power. The balance of power, however it be defined, i.e. whatever the powers were between which it was necessary to maintain such equilibrium, that the weaker should not be crushed by the union of the stronger, is the principle which gives unity to the political plot of modern European history."