These two meeting points or cross-roads have long been, and still are, points of supreme interest to all mankind. At the one all the highways of the Mississippi valley, all the tributaries and sub-tributaries of the great river, meet, and thence they part. At the other all highways between the Atlantic and Pacific focus and intersect. The advancing population and development of the Mississippi valley, and the completion of the Panama Canal, will work together to cause this international interest to grow proportionately in the future. Among the great Powers of the world, no one is concerned so vitally in this progress as is the United States; because of her possession of one of these centers, the mouth of the Mississippi with its huge back country, and because of her geographical nearness to the other. This peculiar interest, which is natural and inevitable in virtue of proximity, is emphasized by the national policy known as the Monroe Doctrine; and still more by the particular result of the Doctrine which has involved the control, administration, and military protection of that belt of Isthmian territory called the Panama Canal Zone. [Illustration: GULF OF MEXICO AND CARIBBEAN SEA] [In the intervening pages, it is shown that the triangle drawn on the map (p. 101) includes all points of strategic importance, these being indicated by black squares. Cuba is the key to the Gulf of Mexico, and also controls three entrances to the Caribbean—the Yucatan, Windward, and Mona Passages. The entrances, the chief points of destination (Jamaica and the Isthmus), and the routes thither, constitute the main objects of military control in the Caribbean.—EDITOR.] ... Taking all together, control over transit depending upon situation only, other conditions being equal, is greatest with Jamaica, next with Cuba, least with the Lesser Antilles. Accepting these conclusions as to control over transit, we now revert to that question to which all other inquiries are subsidiary, namely, Which of the three bases of operations in the Caribbean—one of the Lesser Antilles, Jamaica, or Cuba with its sphere of influence—is most powerful for military control of the principal objective points in the same sea? These principal objectives are Jamaica and the Isthmus; concerning the relative importance of which it may be remarked that, while the Isthmus intrinsically, and to the general interest of the world, is incomparably the more valuable, the situation of Jamaica gives such command over all the approaches to the Isthmus, as to make it in a military sense the predominant factor in the control of the Caribbean. Jamaica is a pre-eminent instance of central position, conferring the advantage of interior lines, for action in every direction within the field to which it belongs.