e 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 invasion to be
opened up as well.

Of course the South had some sea-power of her own. Nine-tenths of
the United States Navy stood by the Union. But, with the remaining
tenth and some foreign help, the South managed to contrive the
makeshift parts of what might have become a navy if the North had
only let it grow. The North, however, did not let it grow.

The regular navy of the United States, though very small to start
with, was always strong enough to keep the command of the sea and
to prevent the makeshift Southern parts of a navy from ever becoming
a whole. Privateers took out letters of marque to prey on Northern
ship