In comprehending the “post-Cold War world,” there are two competing schools of analysis. One – centered in Washington, in foreign ministries, and in the groves of academe – sees a fundamentally sound great-power peace overseen by history’s sole superpower. This view from the top is rational, of a world that follows traditional balance-of-power principles. Politics has become like economics, globalized.

The other school, with a bottom-up view, has its home across the Potomac River at the Pentagon – or rather, not in the Pentagon per se, but among the uniformed military. The closer one is to the frontier of the 21st century – be it in Iraq, Afghanistan, the Balkans, Somalia, the Philippines, or Uzbekistan – the more chaotic, violent, and irrational the world seems. Politics remains barely indistinguishable from war, and is intensely localized.

Most books written about the post-Cold war world, or its cousin, the “post-September 11 world,” tend to reflect the view from the top. The president of the Council on Foreign Relations, Richard Haass – the quintessential foreign policy professional – has a new book out titled “The Opportunity: America’s Moment To Alter History’s Course.” It brims with excruciatingly sensible suggestions for making sure that large and powerful nations get along with one another. Likewise, New York Times columnist Thomas Friedman, the Dr. Johnson of our foreign policy elite, has concluded that, thanks to economic globalization, “The World Is Flat.”

Yet there is no doubt that the best books about the new world and its disorder have so far come from the soldiers and journalists with the bottom up perspective. Former Army officer Ralph Peters is one of these, but the best-known chronicler of the new world disorder has been Robert Kaplan. With his new work, “Imperial Grunts: The American Military on the Ground” (Random House, 421 pages, $27.95), Mr. Kaplan emerges as the Frederic Remington of today’s frontier, a portraitist of lonely American heroes, deep in Injun country.

As Remington is today dismissed as a sentimental romanticizer of American imperial conquest of the West, so Mr. Kaplan has been kept at arm’s length by wonks and intellectuals. Yet through the medium of travel writing and the voices of the soldiers he quotes, Mr. Kaplan captures the simple truths that elude the elites. The short epilogue to “Imperial Grunts” is set, almost too appropriately, in the High Noon Saloon and Brewery in Leavenworth, Kan., where:

nobody talks about “Are we an empire or not?” Rather, people talk about which indigenous armies are better than others, or how successful the Marine training mission in the Caucasus was, tensions between the Army and the Air Force in East Asia, and so on … the talk is about application rather than conceptualization.

The reality is that an increasingly dangerous and unruly world needs policing, and there are precious few forces – precious few people – capable of operating effectively to preserve or create order where there is none. For the moment, moreover, the United States is the only country with the will to take on these tough tasks.

“Imperial Grunts” is an exhibition of fine portraits of the men – and a few women – whom we send to guard our frontiers. There’s Army Colonel Tom Wilhelm, roaming the steppes of Mongolia on a diet of gazelle liver and vodka, building “relationships” with the Mongolian army as the face of American “engagement.” He’s essentially a listening post on the border with China. In this frontier world, even general officers are on their own. In Djibouti, Marine Brigadier General Mastin Robeson, commanding a joint-service task force, spoke “to [regional commander General John] Abizaid a few times a week, and that is the extent of my instructions. It’s great to be ignored. It means you can innovate.”

These are tremendously sympathetic portraits. Mr. Kaplan has immersed himself in military culture and become a keen student of the institutions and the particular service subcultures. He’s alert to the things that matter as much as combat: keeping warm or keeping cool. It’s perhaps the easiest job in journalism to get soldiers to talk, but it takes a lot of work to understand what they’re saying.

Mr. Kaplan frames his portraits less with references to policy debates back inside the Beltway than with grander references from history. The way to measure these soldiers is against the armies of Alexander, Genghis Khan, the British Raj – or, best of all, to their American predecessors in the West or in the Philippines. Less deftly handled, such references might seem pretentious, but set in the Gobi Desert or the lowlands of Colombia, they fit quite comfortably.

Yet the total meaning of Mr. Kaplan’s portraits is left unclear, at least for now; “Imperial Grunts” is meant to be the first in a series of books on modern soldiering. Mr. Kaplan regards imperial grunts as the essential element of American policy in the early 21st century; what’s less certain is whether he regards the policies themselves as wise. Depending on one’s views of American policy in Iraq, for example, you can draw quite different conclusions from Mr. Kaplan’s account of operations in Fallujah. And much has been left out, such as the stories of sailors and airmen who patrol the other parts of the American frontier.

But these are just quibbles. “Imperial Grunts” stands in vivid and bracing counterpoint to most academic analyses of the Pax Americana, circa 2005. Mercifully, it’s also a stylistic counterpoint: “Imperial Grunts” is a great story, very well told.

Mr. Donnelly is a resident fellow in defense and national security studies at the American Enterprise Institute and the editor of Armed Forces Journal.