Moreover, the North was vastly stronger than the South on all the inland waters that were not "Secesh" from end to end. The map shows how Northern sea-power could not only divide the South in two but almost enisle the eastern part as well. Holding the Mississippi would effect the division, while holding the Ohio would make the eastern part a peninsula, with the upper end of 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 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.