and thus enabling large bodies of people to dwell together happily, but also by increasing their military power.  Every nation which has achieved greatness has cultivated assiduously both the arts of peace and the arts of war.  Every nation which has long maintained that greatness has done so by maintaining the policy by which she acquired it. Every nation that has attained and then lost greatness, has lost it by losing the proper balance between the military and the peaceful arts; never by exalting unduly the military, but always by neglecting them, and thereby becoming vulnerable to attack.

In other words, the history of every great nation that has declined shows three periods, the rise, the table-land of greatness, and the decline.  During the rise, the military arts hold sway; on the table-land, the arts of peace and war are fairly balanced; during the decline the peaceful arts hold sway. Facilis descensus Averni.  The rise is accomplished by expending energy, for which accomplishment the possession of energy is the first necessity; the height of the table-land attained represents the amount of energy expended; the length of time that the nation maintains itself upon this table-land, before starting on the inevitable descent therefrom, represents her staying power and constitutes her longevity as a great nation.

How long shall any nation stay upon the table-land?  As long as she continues to adapt her life wisely to her environment; as long as she continues to be as wise as she was while climbing up; for while climbing, she had not only to exert force, she had also to guide the force with wisdom.  So we see that, in the ascent, a nation has to use both force and wisdom; on the table-land, wisdom; in the decline, neither.  Among the nations of antiquity one might suppose that, because of the slowness of transportation and communication, and the feebleness of weapons compared with those of modern days, much longer periods of time would be required for the rise of any nation, and also a longer period before her descent began.  Yet the vast empire of Alexander lasted hardly a day after he expired, and the Grecian cities maintained their greatness but a century and a half; while Great Britain, France, and Germany have been great nations for nearly a thousand years.

Why have they endured longer than the others?

The answer is hard to find; because many causes, and some of them obscure, have contributed to the result.  But, as we observe the kind of constitution and the mode of life of long-lived people, in order to ascertain what kind of constitution and mode of life conduce to longevity in people, so perhaps we may logically do the same with nations.