In the modern historical period the idea of the common superior has been disregarded, and the underlying theory of international intercourse has become that of the "balance of power." The efforts of the diplomatists of this period is to prevent the undue increase of power by any rival country. To increase the power of one's own country, or to prevent the increase of the power of another country, are the causes of the almost constant series of wars throughout this period.

The national unity of England, France, and Spain had been secured by the close of the fifteenth century, but Italy and Germany remained in a divided and chaotic condition, which rendered them a prey to their united neighbors. The invasion of Italy by Charles VIII of France, in 1494, marks the beginning of the Italian wars, which furnish the most convenient beginning to the period of modern history, at least from the standpoint of the study of international law.

1 Wilson and Tucker on International Law, pp. 17-18.