The aim of any discussion such as this should be to narrow down, by a gradual elimination, the various factors to be considered, in order that the decisive ones, remaining, may become conspicuously visible. The trees being thus thinned out, the features of the strategic landscape can appear. The primary processes in the present case have been carried out before seeking the attention of the reader, to whom the first approximations have been presented under three heads. First, the two decisive centres, the mouth of the Mississippi and the Isthmus. Second, the four principal routes, connecting these two points with others, have been specified; these routes being, 1, between the Isthmus and the Mississippi themselves; 2, from the Isthmus to the North American coast, by the Windward Passage; 3, from the Gulf of Mexico to the North American coast, by the Strait of Florida; and, 4, from the Isthmus to Europe, by the Anegada Passage. Third, the principal military positions throughout the region in question have been laid down, and their individual and relative importance indicated. From the subsequent discussion it seems evident that, as "communications" are so leading an element in strategy, the position or positions which decisively affect the greatest number or extent of the communications will be the most important, so far as situation goes. Of the four principal lines named, three pass close to, and are essentially controlled by, the islands of Cuba and Jamaica, namely, from the Mississippi to the Isthmus by the Yucatan Channel, from the Mississippi to the Atlantic coast of America by the Strait of Florida, and from the Isthmus to the Atlantic coast by the Windward Passage. The fourth route, which represents those from the Isthmus to Europe, passes nearer to Jamaica than to Cuba; but those two islands exercise over it more control than does any other one of the archipelago, for the reason that any other can be avoided more easily, and by a wider interval, than either Jamaica or Cuba.