History takes for its field of investigation human events in various
periods of time; anthropo-geography studies existence in various
regions of terrestrial space. But all historical development takes
place on the earth's surface, and therefore is more or less molded by
its geographic setting. Geography, to reach accurate conclusions, must
compare the operation of its factors in different historical periods
and at different stages of cultural development. It therefore regards
history in no small part as a succession of geographical factors
embodied in events. Back of Massachusetts' passionate abolition
movement, it sees the granite soil and boulder-strewn fields of New
England; back of the South's long fight for the maintenance of
slavery, it sees the rich plantations of tidewater Virginia and the
teeming fertility of the Mississippi bottom lands. This is the
significance of Herder's saying that "history is geography set into
motion." What is to-day a fact of geography becomes to-morrow a factor
of history. The two sciences cannot be held apart without doing
violence to both, without dismembering what is a natural, vital whole.
All historical problems ought to be studied geographically and all
geographic problems must be studied historically. Every map has its
date. Those in the Statistical Atlas of the United States showing the
distribution of population from 1790 to 1890 embody a mass of history
as well as of geography. A map of France or the Russian Empire has a
long historical perspective; and on the other hand, without that map
no change of ethnic or political boundary, no modification in routes
of communication, no system of frontier defences or of colonization,
no scheme of territorial aggrandizement can be understood.

[Sidenote: Multiplicity of geographic factors.]

The study of physical environment as a factor in history was