The Types of Frontiers upon which the Military have Operated
First, the natural physical features - mountains, rivers or coasts - limited or re- stricted passage. These were barriers both to the encroaching powers and to raid- ers as were the Pyrenees earlier in French and Spanish history, or the Rhine, or much of the West African coast. But mountains could restrain or shield, and riv- ers could be highways for raiders or pirates to the frustration of the frontier forces whether they were in the army or the coast guard.
Second, there was the maritime or desert frontier, an uncharted area across which the opposing forces had to learn to navigate without much reference to topographical features and in which there were constant natural dangers. This frontier was the domain of frigates and fleets, mobile patrols and fixed forts. Yet across these trackless spaces flowed trade at times and in quantities limited by geography, technology, and the endurance of both man and animals, and this commerce had to be protected. The Athenians, the Phoenicians, the Portuguese, the Spanish, the Dutch, the French and above all the English established their empires by crossing the oceans and using their mobility to create new frontiers on the far shores. So, too, Ghengis Khan, the Moslems, and others from the East used the mobility provided not by the wind but by horses to push their frontiers far from home. The successful crossing of either the sea or the desert was a chal- lenge which in itself gave confidence for battle or other naval or military activi- ties.
Third, there was the frontier of the nucleus state, as in feudal France or Russia, where the state was expanding outward in all directions to obtain control of all territories within its natural or inelastic boundaries. Sometimes this process in- volved conquering neighbors and sometimes, as in France, campaigns to compel nominal vassals to be true ones.
Fourth, the frontier pressing outward into a vacuum, into vast spaces in which a few tribes, often worthy opponents, have occasional settlements was a fluid af- fair. This was the case on land in New France, in New England and in North America generally until the Great Plains were reached, or on the maritime fron- tiers where the Royal and U.S. Navies in the Pacific cruised.
Fifth, was the sieve frontier, the border as it existed at times in America, for many years in the Argentine, and at periods along the North-West Frontier of India, and in Muscovy. It was an ethereal penetrable barrier, a mental line, through which the natives made raids and back across which they were pursued. It marked a fluid state of hunting, raiding and war. The sieve frontier was char- acterized in part by cavalry operations from central reserves because of its ter- rain and because the tribes living there subsisted not by farming but by the raid- ing or raising of cattle. The warlike tribesmen, needing more fluid spaces, were horsemen, or at least far-ranging runners. But the sieve also existed in a more