The ancient amber route across Russia from the Baltic to the Euxine probably guided the Goths in their migration from their northern seats to the fertile lands in southern Russia, where they first appear in history as the Ostrogoths.[184] The caravan trade across the Sahara from the Niger to the Mediterranean coast has itself embodied an historical movement, by bringing out enough negro slaves appreciably to modify the ethnic composition of the population in many parts of North Africa.[185] It was this trade which also suggested to Prince Henry of Portugal in 1415, when campaigning in Morocco, the plan of reaching the Guinea Coast by sea and diverting its gold dust and slaves to the port of Lisbon, a movement which resulted in the Portuguese circumnavigation of Africa.[186] Every staple place and trading station is a center of geographical information; it therefore gives an impulse to expansion by widening the geographical horizon.

The Lewis and Clark Expedition found the Mandan villages at the northern bend of the Missouri River the center of a trade which extended west to the Pacific, through the agency of the Crow and Paunch Indians of the upper Yellowstone, and far north to the Assiniboine and Saskatchewan Rivers.

Here in conversation with British and French fur-traders of the Northwest Company's posts, they secured information about the western country they were to explore.[187] Similarly the trade of the early Jesuit missions at La Pointe near the west end of Lake Superior annually drew the Indians from a wide circle sweeping from Green Bay and the Fox River in the south, across the Mississippi around to the Lake of the Woods and far north of Lake Superior.[188] Here Marquette first heard of the great river destined to carry French dominion to the Gulf of Mexico.
[Sidenote: Movements due to religion.] Trade often finds in religion an associate and coadjutor in directing and stimulating the historical movement.

China regards modern Christian missions as effective European agencies for the spread of commercial and political power.

Jesuit and fur-trader plunged together into the wilds of colonial Canada; Spanish priest and gold-seeker into Mexico and Peru.
American missionary pressed close upon the heels of fur-trader into the Oregon country.