This rise of empires, this coalescence of small groups of men into larger and larger political aggregates, has been the chief work of civilization, when looked at on its political side.[13] Like all the work of evolution, this process has gone on irregularly and intermittently, and its ultimate tendency has only gradually become apparent. This process of coalescence has from the outset been brought about by the needs of industrial civilization, and the chief obstacle which it has had to encounter has been the universal hostility and warfare bequeathed from primeval times. The history of mankind has been largely made up of fighting, but in the careers of the most progressive races this fighting has been far from meaningless, like the battles of kites and crows. In the stream of history which, beginning on the shores of the Mediterranean Sea, has widened until in our day it covers both sides of the Atlantic and is fast extending over the remotest parts of the earth,--in this main stream of history the warfare which has gone on has had a clearly discernible purpose and meaning. Broadly considered, this warfare has been chiefly the struggle of the higher industrial civilization in defending itself against the attacks of neighbours who had not advanced beyond that early stage of humanity in which warfare was chronic and normal. During the historic period, the wars of Europe have been either contests between the industrial and the predatory types of society, or contests incident upon the imperfect formation of large political aggregates. There have been three ways in which great political bodies have arisen. The earliest and lowest method was that of _conquest without incorporation_. A single powerful tribe conquered and annexed its neighbours without admitting them to a share in the government. It appropriated their military strength, robbed them of most of the fruits of their labour, and thus virtually enslaved them. Such was the origin of the great despotic empires of Oriental type. Such states degenerate rapidly in military strength. Their slavish populations, accustomed to be starved and beaten or massacred by the tax-gatherer, become unable to fight, so that great armies of them will flee before a handful of freemen, as in the case of the ancient Persians and the modern Egyptians. To strike down the executive head of such an assemblage of enslaved tribes is to effect the conquest or the dissolution of the whole mass, and hence the history of Eastern peoples has been characterized by sudden and gigantic revolutions.