AS WITH SO MANY geographic terms, the concept of frontiers is closely linked with other ideas. In practice, frontiers rarely remain the same; changing with time and technology, and in the process adjusting the world they have affect upon. It has become common to view frontiers in reference to some political or geographical area that lies beyond the more integrated core of a region and into which expansion could take place. Historically, our image of a frontier often reflected a belief that such places were hostile, empty environments and beyond the reach of settlement. But in a more modern sense, it is more accurate to consider it as peripheral to the primary area of settlement and thus still part of the region as a whole. If we start with this basic idea, we see that frontiers have location, area, boundaries, and some hierarchy. We must also recognize that frontiers can be classified by type, typically political or physical, but they can also be considered as conceptual. Political frontiers tend to be artificial in the sense that they represent expressions of territoriality on the part of sovereign states as they define their boundaries. They are zones of varying width that refer either to the political division between 2 countries (or political groups) or to the settled and uninhabited parts of a country. As such, they are part of political geography. Such political boundaries come about for several reasons, but usually we think of them as 1 of 5 types: pioneer, antecedent, subsequent, superimposed, and relic. There are also natural frontiers, physical features that stand out as natural boundaries between places. For millennia, a system of natural frontiers served as the basis for dividing all types of space. This was particularly so for regions, states, and nations, which often pretended that geography was the sole determinant of the limits of states, and that mountains and rivers were limits established by nature to determine the question of property between nations. Curiously, there never has been even 1 single nation that by virtue of the system of natural frontiers has dreamt of restricting its possessions and the limits of its control. It must be said that natural features (and natural defenses) such as seas, mountains, and rivers can serve very different purposes. There are times when the sea separates nations, and there are times when it unites them. The great Greek historian Horace once called the ocean the great divider of nations. But it is just as easy to see it from the opposite perspective, as the bond of the world. This highlights the fact that over time, barriers perceived to be inaccessible may have a technological basis to their service as a natural barrier. A simple drive is all that is necessary today to cross great mountain ranges or board a plane in Denver and 2 hours later land in San Diego. In each case we must ask ourselves where exactly are the natural frontiers? It is the same story for rivers. The rivers running under bridges are no longer seen as separating nations as they were considered in the days of great city-states. Quite the contrary, they unite them, and instead of being obstacles to overcome they are now viewed as community bonds. Natural frontiers made perfect sense when all forms of transportation were limited to muscle power and the world was a system of land-based nations. But once you add sources other than muscle power to transportation, the usefulness of natural boundaries as markers for the extent of a nation’s frontier comes quickly into question. Major changes in technology have usually resulted in major changes in transportation geography. As you redefine space in terms of time, you also redefine it in terms of distance. If you have ever used the phrase “it’s a small world” you know that which was far away even 100 years ago, is right next door today. A frontier today is the opposition and the contrast of peoples. It is not the Pyrenees, which separates France from Spain, as much as it is the difference in manners, habits, and customs between the 2 areas. Ideas such as this help clarify the fact that conceptual frontiers reflecting the wants and needs of people play an active role in determining how we view both political and physical frontiers. This does not mean that frontiers no longer exist, for they clearly do. But the scale at which we define them has changed on all levels, as well as has our purpose in determining what frontiers are. Things considered to be science fiction by Jules Verne have become reality. Politically, we have passed from that which was considered empire to kings and emperors to that which is the empire for multinational corporations. Now boundaries in time and space are reflected as inefficiencies in the market; as costs that hinder the degree to which nations develop. In many respects, the wish to fix boundaries is out of date. In a century where we talk of colonizing other planets and lay plans for ventures to Mars, it is the will of nations that determines frontiers, not nature. Nations make their frontiers; nations themselves create the barriers that exist between themselves and their neighbors. It is also out of this dominance of the land that a new global perspective has grown, for as the power to dominate nature and eliminate frontiers has expanded, so has the understanding that it has not been done without tremendous environmental cost. This unity of environmental consciousness extends far beyond the traditional politico-geographic realm, where coalitions of states now discuss the consequences of global action. The rapid elimination of space as the ultimate barrier has given territory and frontiers new meaning. In an increasingly global world economy, frontier lands whose sparse populations once served as ideal buffers against outside invasion must now be made part of the whole. Today, the entire geopolitical model as laid out by Halford J. Mackinder has been inverted. Now, instead of providing some type of insular space as a means of preserving a nation’s status, frontier space is a threat to national unity if not made a convincing and functional part of the national consciousness. For regions to remain sustainable, they must have some coherent principle, some organizing factor, focal point, or purpose. This relationship has typically taken the form of the core-periphery model, with a central community or economic driving force defining the core and a less well-defined zone or zones of dependency arrayed around the core. As regions mature, frontier areas pass into the domesticated landscape. New communities must now be founded in locations other than those defined by ideal topography. Two hundred years ago, frontiers were seen as vital to stability in the geopolitical world. Today, frontiers are viewed as the biggest obstacles.