INFLUENCES OF ENVIRONMENT 149 



have pressed long series of barbarian invaders from At- 

 tila the Hun to the Turkish besiegers of Vienna in 1683. 

 The river is a great natural highway to which every 

 neighboring state desires access. In America, the Mo- 

 hawk depression through the northern Appalachians 

 diverts a significant amount of Canada's trade from the 

 Great Lakes to the Hudson. 33 Formerly it enabled the 

 Dutch traders at New Amsterdam to tap the fur trade 

 of Canada's forests, and later after the construction of 

 the Erie canal, enabled New York to defy the competi- 

 tion of Boston, Philadelphia and Baltimore, in provid- 

 ing tne easiest outlet for the commerce of the rich Ohio 

 valley. The Cumberland Gap was the natural avenue 

 to the West from Virginia and the Carolinas. Buffalo, 

 Indian and pioneer have successively followed this 

 route. 34 Natural conditions have fixed channels in which 

 the stream of humanity most easily moves. 35 The direc- 

 tion of mountain ranges determines within certain limits 

 the destination of migration and this tends to keep suc- 

 ceeding waves to the old channels. These lines of least 

 resistance are first sought out and only when they are 

 blocked or preempted do the invaders turn to more diffi- 

 cult paths. 



The long and narrow valley of the Nile, with its fertile 

 hem of flood-plain on either bank and the protecting bar- 

 rier of the great desert beyond, furnished conditions 

 favorable to the development of a great civilization. 

 Here was a rich soil kept in splendid condition by the 

 annual flood period which replenished the vital mineral 

 and organic elements withdrawn by the crops, so that 



33 Semple, op. cit., p. 5. 



3 * Semple, E. C. American History and Its Geographic Conditions, p. 68. 



36 See figure 53. 



