First, the contemporary battlefield is more likely to be urban and congested, rather than wide open and sparsely populated. Rarely will adversaries cooperate in fulfilling the American preference for long-range tank battles fought in the desert under skies dominated by American fighter-bombers and attack helicopters. The 2003 invasion of Iraq was an exception; the urban battles of the occupation that followed were closer to the rule.

Second, and by extension, the Pentagon’s investment in conventional warfare will continue to have little relevance in the sort of conflicts confronting American forces. The p rimary challenge is less to defeat armies than to control populations. Pacification rather than sustained close combat absorbs soldiers’ energy and attention. The greater part of the warrior’s role involves not killing but muting the antagonism caused by the warrior’s own unwelcome presence.

Third, if American forces find it difficult to adjust to the peculiar demands of such wars, then those responsible for formulating basic national security policy should consider the possibility that the wars themselves just might be futile.

Since 1993, the United States has killed any number of “skinnies” and “sammies,” not to mention innocent bystanders, in Afghanistan, Iraq, Libya, Yemen, Syria and even back in Somalia, where drone strikes and Special Forces routinely target those who have succeeded Mr. Aidid in contesting the control of that country. Rarely does an American leader, political or military, explain what larger purpose these wars are serving. Never do they venture to speculate on when they might end.

Why was it necessary for the 18 Americans to die in a failed effort to dictate the future of Somalia? What purpose did their sacrifice serve? A quarter-century later, these questions have lost none of their pertinence. If anything, they have become more urgent.

In retrospect, the lessons to be taken from this small but immensely instructive episode appear obvious. In retrospect, lessons always do.

Yet with a bit more effort and perhaps a generous dose of humility, the United States might have discerned those lessons at the time. Applying them to subsequent military endeavors might have alleviated or even eliminated the failures and frustrations that have become the principal themes of recent American military history.

Instead, America’s leaders chose to ignore it — the sooner forgotten the better. This turned out to be a profound oversight, and the troops whom Americans profess to admire have since paid a high price for it.

Andrew J. Bacevich is the author of the forthcoming book “Twilight of the American Century.”

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