Fleets of the Islanders could no more penetrate into the Baltic than they could into the Black Sea.
The Heartland, for the purposes of strategical thinking, includes the Baltic Sea, the navigable Middle and Lower Danube, the Black Sea, Asia Minor, Armenia, Persia, Tibet, and Mongolia. Within it, therefore, were Brandenburg-Prussia and Austria-Hungary, as well as Russia—a vast triple base of man-power, which was lacking to the horse-riders of history. The Heartland is the region to which, under modern conditions, sea-power can be refused access, though the western part of it lies without the region of Arctic and Continental drainage. There is one striking physical circumstance which knits it graphically together; the whole of it, even to the brink of the Persian Mountains overlooking torrid Mesopotamia, lies under snow in the winter time. The line indicative of an average freezing temperature for the whole month of January passes from the North Cape of Norway southward, just within the 'Guard' of islands along the Norwegian shore, past Denmark, across Mid-Germany to the Alps, and from the Alps eastward along the Balkan range. The Bay of Odessa and the Sea of Azof are frozen over annually, and also the
