In this new, challenging political landscape where the possession of potent military arsenals can be upstaged by the ownership of mammoth reserves of oil, natural gas, and other sources of primary energy, the United States has found itself scrambling - on the battlefield, on global trading floors, and in diplomatic back rooms - to somehow come to terms with what Sen. Richard G. Lugar (Rep-Indiana) has termed "petro-superpowers" - nations that wield disproportionate power in the international system by virtue of their superior energy reserves.

Other major energy-consuming nations have also been forced to adjust to this changing landscape. China, is becoming ever more dependent on imported petroleum and so must scour the world for available supplies. Japan, with the world's second largest economy - yet even more dependent on imported energy supplies than China-has found itself locked in fierce competition with Beijing for access to some of the same overseas reserves.

On the other side of the ledger, energy-rich states like Kazakhstan and Nigeria have come to enjoy greater leverage in world affairs, attracting a constant stream of high-level visitors from energy-consuming nations - often bearing promises of investment financing, military aid, and other forms of largess. The outspoken president of Venezuela, Hugo Chávez, has appeared immune to US retaliation despite his frequent verbal attacks on the Bush administration and his close association with the leaders of "pariah" states such as Cuba, Iran, and Syria.

Why has energy come to play such a pivotal role in world affairs? To begin with, its continued availability - in great profusion - has never been as critical to the healthy operation of the global economy. Energy is required to keep the factories humming, power the cities and suburbs that house the world's rising population, and produce the crops that feed the planet. Without an increase in energy available in the years to come, the world economy will fall into recession or depression, the globalization project will fail, and the planet could descend into chaos.

But the wheels of industry are not the only ones to slow without an abundant supply of energy; military forces are equally dependent on a copious infusion of critical fuels. For major powers like the United States that rely on airpower and mechanized ground forces to prevail in conflict, the need for petroleum products multiplies with each new advance in weapons technology.

At the same time, the competition for energy has never been so intense. "Energy developments in China and India are transforming the global energy system by dint of their sheer size and their growing weight in international fossil-fuel trade," the International Energy Agency (IEA) reported in its World Energy Outlook for 2007. Despite huge investment in new oil-production capacity additions, "it is very uncertain whether they will be sufficient to compensate for the decline in output at existing fields and keep pace with the projected increase in demand." Hence, an intense and sometimes brutal competition for untapped supplies has erupted.

Besides, an increasing body of evidence suggests that the era of "easy oil" is over and that we have entered a new period of "tough oil." Each new barrel added to global reserves, experts suggest, will prove harder and more costly to extract than the one before; it will be buried deeper underground, farther offshore, in more hazardous environments, or in more conflict-prone, hostile regions of the planet. A similar scenario is likely to play out when it comes to most other existing fuels, including coal, natural gas, and uranium. Given this, the future adequacy of global energy stocks is in serious doubt.

Scientists are avidly seeking ways to develop a new spectrum of fuels to replace those now at risk of depletion while releasing far fewer or zero climate-altering "greenhouse gases" into the atmosphere. But no major energy-consuming nation has yet devoted sufficient resources to this problem to ensure that these alternatives will be available on a large enough scale to replace existing energy sources in the foreseeable future. With both old and new consumers reliant on these traditional fuels-and no practical, plentiful alternatives in sight-the struggle over them is certain to be fierce.

As a result, the problem of "energy security" - as it is widely termed - has climbed toward the top rung of the international ladder of unease and concern. Not surprisingly, this has fundamentally changed the perception of what constitutes "power" and "influence" in a dramatically altered international system, forcing policymakers to view the global power equation in entirely new ways.

Michael T. Klare is a professor of peace and world-security studies at Hampshire College, a Foreign Policy In Focus columnist, and the author of "Rising Powers, Shrinking Planet: The New Geopolitics of Energy" (Metropolitan Books, 2008).

This essay is a shorter version of the article published on May 6 in Foreign Policy in Focus, and drawn from M.T. Klare's new book "Rising Powers, Shrinking Planet: The New Geopolitics of Energy", published by Metropolitan Books.

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