But it is also a link in a great chain of lands, and therefore may feel a shock or vibration imparted at the remotest end.

The gradual desiccation of western Asia which took a fresh start about 2,000 years ago caused that great exodus and displacement of peoples known as the _Voelkerwanderung_, and thus contributed to the downfall of Rome; it was one factor in the Saxon conquest of Britain and the final peopling of central Europe.

The impact of the Turkish hordes hurling themselves against the defenses of Constantinople in 1453 was felt only forty years afterward by the far-off shores of savage America.
Earlier still it reached England as the revival of learning, and it gave Portugal a shock which started its navigators towards the Cape of Good Hope in their search for a sea route to India.

The history of South Africa is intimately connected with the Isthmus of Suez.

It owes its Portuguese, Dutch, and English populations to that barrier on the Mediterranean pathway to the Orient; its importance as a way station on the outside route to India fluctuates with every crisis in the history of Suez.
[Sidenote: Direct and indirect effects of environment.] The geographic factors in history appear now as conspicuous direct effects of environment, such as the forest warfare of the American Indian or the irrigation works of the Pueblo tribes, now as a group of indirect effects, operating through the economic, social and political activities of a people.