Not that the communists cared. They had contempt for the peasants and alienated them further by extorting food and reinforcements through threats and executions. They burned villages in hopes of making the peasants a burden on the U.S.-backed government and crippling the Greek economy.

In July 1949, Tito shut the Yugoslav border, eliminating Yugoslavia as a sanctuary. But Joes argued that, by then, the insurgents were doomed anyway. "They had already shot themselves in the feet and both knees," he said. In Iraq, U.S. and Iraqi troops have embarked on an offensive in the west partly in hopes of cutting off what the military command says is a flow of foreign fighters and materiel across the Syrian border. But military experts say that without stationing thousands of troops along the border, the military has little chance of closing it off.

An opaque region

If the immediate objective of the insurgents is relatively limited — not to topple the government and drive the Americans out now but to pin them down and bleed them — that at least would have solid precedents. As the counterterrorism expert Bruce Hoffman noted in a paper for Rand last year, "For more than 30 years, a dedicated cadre of approximately 200 to 400 IRA gunmen and bombers frustrated the maintenance of law and order in Northern Ireland, requiring the prolonged deployment of tens of thousands of British troops." Yet the IRA is still far from its larger goal: to drive the British out.

Among Iraq's insurgents, the jihadists are one group that has suggested a sweeping goal. They want to establish a new caliphate — a religious regime with expansive boundaries. For them, the destruction and chaos in Iraq may represent creative forces, means of heightening the contrasts among sects, religions and whole civilizations. Searching for parallels, several experts compared the insurgents in Iraq to the violent anarchists of the late 19th and early 20th centuries. That movement took root among the alienated and uprooted who could find no place in modern society.

Yet it may prove to be one of history's humbling lessons that history itself fails to illuminate the conflict under way in Iraq. No one really knows what the insurgents are up to.

"It clearly makes sense to the people who are doing it," said Dr. Loren B. Thompson, a defense analyst at the Lexington Institute. "And that more than anything else tells us how little we understand the region."