the isthmus safe in Northern hands between Pittsburgh, the great
coal and iron inland port, and Philadelphia, the great seaport,
less than three hundred miles away. The same isthmus narrows to
less than two hundred miles between Pittsburgh and Harrisburg (on
the Susquehanna River); and its whole line is almost equally safe
in Northern hands. A little farther south, along the disputed
borderlands, it narrows to less than one hundred miles, . from
Pittsburgh to Cumberland (on the Potomac canal). Even this is not
the narrowest part of the isthmus, which is less than seventy
miles across from Cumberland to Brownsville (on the Monongahela)
and less than fifty from Cumberland to the Ohiopyle Falls (on the
Youghiogheny). These last distances are measured between places
that are only fit for minor navigation. But even small craft had
an enormous advantage over road and rail together when bulky
stores were moved. So Northern sea-power could make its
controlling influence felt in one continuous line all round the
eastern South, except for fifty miles where small craft were
concerned and for two hundred miles in the case of larger
vessels. These two hundred miles of land were those between the
Ohio River port of Wheeling and the Navy Yard at Washington.

Nor was this virtual enislement the only advantage to be won. For
while the strong right arm of Union sea-power, facing northward
from the Gulf, could hold the coast, and its sinewy left could
hold the Mississippi, the supple left fingers could feel their
way along the tributary streams until the clutching hand had got
its grip on the whole of the Ohio, Cumberland, Tennessee,
Missouri, Arkansas, and Red rivers. This meant that the North
would not only enjoy the vast advantages of transport by water
over transport by land but that it would cause the best lines of