Global warming already is changing the way global wars are going to be fought -- and the weapons they are going to be fought with.

Since the end of the Cold War, the United States, as the global hyperpower, has set the fashion for military establishments around the world. The tradition of American war-making has always been high-tech, at least back to President Abraham Lincoln's enthusiasm for every form of new technology during the Civil War.

The electric telegraph and the railroad proved crucial, and Lincoln, a former railroad lawyer who obsessively prowled the White House telegraph room across Pennsylvania Avenue from the White House, was well versed in both of them.

Over the past two decades the deeply rooted U.S. obsession with cutting-edge technology has shaped the composition of the U.S. armed forces probably more than any other factor. And because the United States seemed free of major threats, at least until Sept. 11, 2001, there was broad consensus across the political spectrum that the United States no longer needed large standing armies, especially when wonderful new communications, targeting and information technology could do the job.

Even after the al-Qaida terrorist attacks of Sept. 11, 2001, killed more Americans than died at Pearl Harbor in December 1941, this trend toward smaller military establishments, fewer soldiers and far more high tech accelerated rather than slowed. Donald Rumsfeld, U.S. defense secretary for the first six years of President George W. Bush's presidency, was an enthusiastic champion of high-tech wonder weapons of every kind, and he staffed the Pentagon with neoconservative intellectuals who, as Max Boot claimed in the title of his book, believed in the idea of "War Made New." They were convinced that the very nature of conflict had been transformed lastingly in America's favor by U.S. dominance in advanced technology.

However, these beliefs did not merely shape the U.S. Department of Defense: They lastingly influenced procurement policies and strategic planning in all the other major industrialized democracies as well.

Even Russia worked hard to cut down the size of its armed forces and make them fast-reacting and high-tech, though with mixed results. The Russians proved quite successful with the design and production of their fourth-generation combat aircraft, but the Russian army and special forces remained large, poorly trained forces that operated dismally in the face of terrorist attacks. However, the August 2008 five-day blitzkrieg in which the Russian army conquered one-third of the mountainous, heavily forested former Soviet republic of Georgia suggested that years of massive investment and intense efforts at modernization were starting to pay off.

But the now well-documented phenomenon of global climate change has transformed all these calculations. Combined with continuing global population growth, especially in the developing world, climate changes have made much of sub-Saharan Africa unsustainable for the scale of population it supports. Prosperous nations and regions like the European Union, the United States and Saudi Arabia are now forced to deal with enormous influxes of illegal immigrants every year. The United States and Saudi Arabia, in particular, have reacted to this by strengthening their border barriers and defenses. But having effective borders requires lots of soldiers to man them.

(Part 2: The growing need for larger, low-tech armies)