In the Gettysburg Address, Abraham Lincoln used three of its 272 immortal words to describe the military cataclysm engulfing our nation as “a great civil war.”

Thirty-six years later, the United Daughters of the Confederacy voted a resolution mandating members call it the War Between the States. For his part, Frederick Douglass referred to the Abolition War while some Texans insist to this day on the War of Northern Aggression. One aficionado has tallied 120 different terms.

Not until 1907 did the U.S. Congress agree the official name would be the “Civil War,” reports Harvard University historian David Armitage in his bracing and nuanced “Civil Wars: A History in Ideas.”

Nomenclature matters. “Where a philosopher, a lawyer, or even a political scientist might find only confusion in the disputes over the term ‘civil war,’ a historian scents opportunity,” Armitage writes. “All definitions of civil war are necessarily contextual and conflictual. The historian’s task is . . . to ask where such competing conceptions come from.”

It turns out to be a dense and fascinating tale. Armitage, British-born and Cambridge-educated, undertakes a close reading of 2,000 years of contested meanings circling the notion of civil war.

Anyone trying to parse Syria’s current military conflagration will find time with “Civil Wars” well spent. Its unchecked slaughter stems partly from the wider world’s bedevilment over how to categorize the fighting — noble resistance or wanton terrorism, as President Bashar al-Assad would have it, or some mishmash in between?

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Still, what has been notoriously hard to pin down legally and philosophically is gaining on us. “Civil war has gradually become the most widespread, the most destructive, and the most characteristic form of organized human violence,” Armitage writes. While 2014 clocked only one interstate conflict, a dustup between India and Pakistan with fewer than 50 casualties, “since 1989, an average of twenty intrastate wars have been in progress at any moment — about ten times the annual average globally between 1816 and 1989.”

Since 1945, these civil conflicts have killed an estimated 25 million combatants, about half the casualties of World War II. “The material and economic costs have been no less staggering,” Armitage writes, ticking off displacement, disease, squandered resources, lost civilian life. “Not without reason, then, has civil war been chillingly described as ‘development in reverse.’”

Armitage, being a historian, likes to look for beginnings. The first third of his book centers on ancient Greece and particularly Rome, where he pins the originating concept of civil war to the first century BCE “Columns and capitols, amphitheaters and aqueducts, laws and Latin, would not be the only legacies of Rome to the world; among the most enduring, and the most unsettling, was the category of civil war itself. Indeed, for more than a millennium and a half, civil war was viewed through Rome-tinted spectacles.”

One thrill of this book is its erudition — almost all the translations are Armitage’s own. In the middle section, “Early Modern Crossroads,” he deals with European ideas of conflict between the 16th and 18th centuries. Noting the “theme of civil war is central to Shakespeare’s entire body of work,” Armitage points out that many of the ancient historical accounts “Augustine had studied in North Africa in the fourth century C.E. would have been familiar to the young William Shakespeare (1564-1616) at his grammar school in Stratford-upon-Avon over a thousand years later.”

The book can feel like a daisy chain built from the cerebral cortex of one Western man to the next. (Armitage mentions the Arabic term fitna and the Chinese concept of nei zhan, or internal war, but places these traditions outside his scope.) The final section is called “Paths to the Present” and leads to a lively chorus: Dean Acheson, Thomas Hobbes, Karl Marx, Michel Foucault, John Rawls and the ever-handy Michel de Montaigne. For such a murderous topic, the pages are more legalistic than bloody.

The fine, clear writing helps: “Civil war was not a fact of nature, waiting to be discovered,” Armitage insists, allowing that it can feel that way.

As hard as it is to imagine vanquishing civil war, the author audaciously suggests it: “It is my aim to show that what humans have invented, they may yet dismantle; that what intellectual will has enshrined, an equal effort of imaginative determination can dethrone.”

That would be revolution indeed.