Some of the ancient empires continued for long periods.  The history of practical, laborious, and patient China is fairly complete and clear for more than two thousand years before our era; and of dreamy, philosophic India for almost as long, though in far less authentic form.  Egypt existed as a nation, highly military, artistic, and industrious, as her monuments show, for perhaps four thousand years; when she was forced by the barbarians of Persia into a condition of dependence, from which she has never yet emerged.  The time of her greatness in the arts and sciences of peace was the time of her greatest military power; and her decline in the arts and sciences of peace accompanied her decline in those of war.  Assyria, with her two capitals, Babylon and Nineveh, flourished splendidly for about six centuries, and was then subdued by the Persians under Cyrus, after the usual decline.  The little kingdom of the Hebrews, hardy and warlike under Saul and David, luxurious and effeminate under Solomon, lasted but little more than a hundred years.  Persia, rising rapidly by military means from the barbarian state, lived a brilliant life of conquest, cultivated but little those arts of peace that hold in check the passions of a successful military nation, yielded rapidly to the seductions of luxury, and fell abruptly before the Macedonian Alexander, lasting less than two hundred and fifty years.  Macedonia, trained under Philip, rose to great military power under Alexander, conquered in twelve years the ten most wealthy and populous countries of the world—­nearly the whole known world; but fell to pieces almost instantly when Alexander died.  The cities of Greece enjoyed a rare pre-eminence both in the arts and sciences of peace and in military power, but only for about one hundred and fifty years:  falling at last before the superior military force of Macedon, after neglecting the practice of the military arts, and devoting themselves to art, learning, and philosophy.  Rome as a great nation lasted about five hundred years; and the last three centuries of her life after the death of Commodus, about 192 A. D., illustrate curiously the fact that, even if a people be immoral, cruel, and base in many ways, their existence as an independent state may be continued long, if military requirements be understood, and if the military forces be preserved from the influence of the effeminacy of the nation as a whole.  In Rome, the army was able to maintain a condition of considerable manliness, relatively to the people at large, and thus preserve internal order and keep the barbarians at bay for nearly three hundred years; and at the same time exert a powerful and frequently deciding influence in the government.  But the effeminacy of the people, especially of those in the higher ranks, made them the creatures of the army that protected them.  In some cases, the Emperor himself was selected by the army, or by the Pretorian Guard in Rome; and sometimes the guard removed an Emperor of whom it disapproved by the simple expedient of killing him.