FOR CAUSE AND COMRADES: Why Men Fought in the Civil War.<i> By James M. McPherson</i> .<i> Oxford University Press: 256 pp., $25</i>

There are many reasons why the Civil War continues to fascinate us. To begin with, it had a profound political significance. If the American Revolution gained us freedom from British rule and enabled us to launch our experiment in democracy, it was the Civil War that put the experiment on solid footing. The union of states was greatly strengthened. “The ropes of sand,” as a period writer put it, “were replaced by wire cables.” The blot of slavery, so foreign to the affirmation that “all men are created equal,” was eradicated.

These results of the war were noted throughout the world, gaining our young nation a firm respect and raising prospects for a wider seeding of democracy.

Aside from its lustrous political implications, the war was especially rich in human interest. Seldom has a military stage been trod by so many colorful personalities, so many people of outstanding suitability to their work. Some of the principals, among them Abraham Lincoln, Robert E. Lee, Stonewall Jackson and Jeb Stuart, seem larger than life. And countless of the war’s events were highly dramatic. Considered today, many of these dramas, though known to be filled with suffering and death, seem tinged with romance. We learn they were sidelighted with amusing episodes, chivalrous acts and friendly moments between foes, and these contemplations charm us.

We are moved by the knowledge that the war commonly disrupted family ties and separated friends. People who had deep affection for each other were committed to doing each other harm. Many Union and Confederate officers had been the closest of friends in the old Federal service, had fought shoulder-to-shoulder in the Mexican War and had shared the rigors and hazards of outpost duty on the western frontier. The Civil War turned these friends into deadly opponents.

But no facet of the war prompts more fascination than the phenomenal courage shown by the more dedicated segment of the 3 million men from the North and South who were signed up during the four years of fighting. Many thousands were in it from beginning to end, their spirit unremitting in the face of battlefield dangers and horrors, health risks posed by a variety of diseases, suffering caused by exposure to extremes of weather, repeated marches of a punishing nature, severe food and supply shortages and intense longing for home and family.

Some insisted on staying in the service after receiving wounds that should have sent them home for good. There were even those who did this more than once. Most notable of all was the general willingness of the men to take part, time and again, in extremely perilous charges. This kind of spirit is not easy for us to comprehend, and we react with questions. How could ordinary mortals endure four years of an existence so heavily laced with hellish experiences? What motivated these soldiers?

James M. McPherson addresses these questions in “For Cause and Comrades.” A professor of history at Princeton University and longtime Civil War scholar and author, McPherson is well qualified for this project. He won the Pulitzer Prize in 1989 for his best-selling history of the war, “Battle Cry of Freedom,” and is a writer who is meticulous in his research and objective in his conclusions.

In “For Cause and Comrades,” he advances many of his points by allowing the soldiers to speak for themselves. He chose as his speakers 1,076 men--647 Federals and 429 Confederates--studying more than 25,000 letters and 249 diaries to glean his material, the selection being as representative as he could make it.

There is great historical value in the letters and diaries of Civil War soldiers. Military censorship was practically nonexistent. The men usually said exactly what they wanted to say. To be sure, most were not skilled grammarians. But many of the writers expressed themselves clearly, some even eloquently, and there was a widespread understanding of both the political and military situations.

Appreciation for the nation’s origins was universal, thanks to its glorification by prewar authors and teachers of history. And the issues that led to the war had been topics of public discussion for many years before the first shots were ever fired. During the four years of fighting, the soldiers followed military and political developments by reading the newspapers. There was even a regular exchange of papers between soldiers from the North and the South.

McPherson’s speakers reveal that both sides considered themselves to be fighting for the preservation of liberty--Northerners for the survival of the republic and Southerners for the right to conduct their affairs as they saw fit without being regulated in Washington, where their political power had been waning.

The Southern conception of freedom included the right to maintain the slave system, an irony that is not altogether beyond understanding. The Southern economy, largely agrarian, had developed in such a way as to become dependent upon the system. There were, of course, many people of conscience in the South, but even most of these had no other thought than to put the economy first. Arguments were devised to justify slavery. From the Christian community, for example, came the remarkable claim that the system performed the great good of bringing the Africans from heathenism to Christ. In the industrial North, slavery had never become a component of prosperity. It was viewed, in fact, as a threat to jobs. Therefore it wasn’t hard for Northerners to take a moral stand against the institution.

McPherson convincingly maintains that the chief reason so many Civil War soldiers fought so long and so resolutely was that they had an iron belief in their goals. Each side regarded itself as engaged in a holy crusade, supremely important not only to the current generation but also to those ahead. Loyalty, duty and courage were revered qualities. When these soldiers said they were willing to die for their cause, they meant it. Proof of this can be found in the war’s horrendous casualty figures.

There is a troubling aspect to McPherson’s book. If we admit our incomprehension of Civil War courage and are obliged to rely on a scholar to explain it to us, we are obviously ill-prepared to deal with a military emergency that might require such a spirit. It’s true that something very near to it was roused during World War II. Although we voiced few patriotic sentiments during that conflict, we embraced the cause with a will, made many sacrifices for it and fought with all the courage and determination needed to prevail. More than 50 years later, however, the question might well be asked: Is there mettle enough within us today to enable us to respond with sufficient zeal to a new threat to our heritage? McPherson believes this question is unanswerable. “One hopes,” he says, “that it will remain unanswered.”

This is a very sensible hope. But perhaps as we read his book, we should try to overcome our wonder at the kind of courage it chronicles and try to identify with it.