The lines of expansion followed by the French and English in the settlement of America and also the extent of territory covered by each were powerfully influenced by geographic conditions.  The early French explorers entered the great east-west waterway of the St. Lawrence River and the Great Lakes, which carried them around the northern end of the Appalachian barrier into the heart of the continent, planted them on the low, swampy, often navigable watershed of the Mississippi, and started them on another river voyage of nearly two thousand miles to the Gulf of Mexico.  Here were the conditions and temptation for almost unlimited expansion; hence French Canada reached to the head of Lake Superior, and French Louisiana to the sources of the Missouri, To the lot of the English fell a series of short rivers with fertile valleys, nearly barred at their not distant sources by a wall of forested mountains, but separated from one another by low watersheds which facilitated lateral expansion over a narrow belt between mountains and sea.  Here a region of mild climate and fertile soil suited to agriculture, enclosed by strong natural boundaries, made for compact settlement, in contrast to the wide diffusion of the French.  Later, when a growing population pressed against the western barrier, mountain gates opened at Cumberland Gap and the Mohawk Valley; the Ohio River and the Great Lakes became interior thoroughfares, and the northwestern prairies lines of least resistance to the western settler.  Rivers played the same part in directing and expediting this forward movement, as did the Lena and the Amoor in the Russian advance into Siberia, the Humber and the Trent in the progress of the Angles into the heart of Britain, the Rhone and Danube in the march of the Romans into central Europe.

[Sidenote:  Segregation and accessibility.]

The geographical environment of a people may be such as to segregate them from others, and thereby to preserve or even intensify their natural characteristics; or it may expose them to extraneous influences, to an infusion of new blood and new ideas, till their peculiarities are toned down, their distinctive features of dialect or national dress or provincial customs eliminated, and the people as a whole approach to the composite type of civilized humanity.  A land shut off by mountains or sea from the rest of the world tends to develop a homogeneous people, since it limits or prevents the intrusion of foreign elements; or when once these are introduced, it encourages their rapid assimilation by the strongly interactive life of a confined locality.  Therefore large or remote islands are, as a rule, distinguished by the unity of their inhabitants in point of civilization and race characteristics.  Witness Great Britain, Ireland, Japan, Iceland, as also Australia and New Zealand at the time of their discovery.  The highlands of the Southern Appalachians, which form the “mountain backyards” of Kentucky, Tennessee and North