James McPherson (right) is the George Henry Davis ‘86 Professor of American History at Princeton University. He was the 2000 Jefferson Lecturer in the Humanities and president of the American Historical Association in 2003.

America’s leading historian of the Civil War, he won the 1989 Pulitzer Prize forBattle Cry of Freedom, a New York Times best seller that has sold more than six hundred thousand copies. His bookCrossroads of Freedom: Antietam(2002) was also a New York Times bestseller, and he won the 1998 Lincoln Prize forFor Cause and Comrades. His many Civil War publications have been widely hailed as the catalyst for such films as Glory and Gettysburg and the television documentary The Civil War by Ken Burns. He has authored more than a dozen books and more than 100 articles about the Civil War and the Civil War era. He also coauthored Britannica’s biography of Ulysses S. Grant and wrote a sidebar for Britannica on Grant’s Personal Memoirs. On the occasion of Lincoln’s 200th birthday, he kindly consented to the following interview, with questions posed by Britannica senior editor Jeff Wallenfeldt.

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Britannica: You point out that Abraham Lincoln himself noted in a Congressional speech that his military experience was limited to battling mosquitoes during brief service in the Black Hawk War. How was he able to transform himself into a military leader, and what lessons might his experience offer for Barack Obama, who ascends to the post of commander in chief without having served in the military?

McPherson: Lincoln learned the job of military leadership as commander in chief by reading works on military history and strategy, by asking questions of anyone who had any kind of expertise, such as the first general in chief, Winfield Scott, Quartermaster-General Montgomery Meigs, naval captain (later admiral) John Dahlgren, and others even including George McClellan. As a self-taught lawyer who also once mastered Euclidean geometry on his own for mental exercise, Lincoln had a probing, questing mind and experience as a trial lawyer in cross-examining people. He was also capable of learning from his mistakes (and the mistakes of others). Obama seems to have many of the same personal and intellectual qualities, and like Lincoln he will undoubtedly learn from reading and talking with people who have expertise in the subject and will absorb their insights and then transform them into policy and strategy, as Lincoln did.

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Britannica: You have indicated that a big reason for writingTried by Warwas that the subject of Lincoln’s military stewardship of the American Civil War had been understudied since T. Harry Williams’s Lincoln and His Generals (1952). Was Lincoln’s hands-on involvement with the strategic conduct of the war well known at the time (and, if so, approved of) by the public and Congress? How did the generals feel about his active role?

McPherson: Yes, Lincoln’s hands-on involvement with military strategy and command was well-known at the time. Reactions to that involvement tended to follow partisan lines: Democrats condemned it, especially what they regarded as interference with McClellan, and Republicans not only supported it but sometimes demanded that Lincoln ride herd over the military (many generals were Democrats in background) more thoroughly. During the McClellan regime (July 1861-November 1862) most generals in the Army of the Potomac resented Lincoln’s oversight of their actions. The legacy of resentment persisted somewhat less openly among subsequent commanders of the Army of the Potomac and their staffs, until Ulysses S. Grant became general in chief in March 1864. Lincoln exercised less direct oversight of Western armies, except for the Army of the Ohio under Buell and, to some degree, the successor Army of the Cumberland under Rosecrans. Successful generals were not as subject to this oversight–largely because they were successful, and Lincoln was content to support rather then second-guess them–this was particularly true in the case of Grant and then Sherman as commanders of the Army of the Tennessee. But in the case of Grant, Lincoln repeatedly intervened to protect him against his numerous critics, and to support him through thick and thin–one of the most important contributions Lincoln made to ultimate Union victory.

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Britannica: In his determination to find a commanding general who could lead the Union Army to victory, Lincoln was willing to overlook Gen. George McClellan’s disdain for him and Gen. Ulysses S. Grant’s reputation for drunkenness. What convinced Lincoln that McClellan was the wrong man and Grant the right man for the job?

McPherson: McClellan’s main defect was his unwillingness to take risks–to confront that terrible moment of truth when one must confront the enemy on the battlefield. He was superb at organizing and training troops, at logistics, at fostering esprit among his soldiers, but he lacked what was then called “moral courage”–the courage to act instead of merely to react. Lincoln soon perceived this weakness, and at first tried to deal with it by bucking up McClellan’s moral courage, then by giving him peremptory orders, but finally recognized that McClellan was not going to change, and dismissed him because, as Lincoln put it, he was tired of trying to bore with an augur too dull to take hold. Grant, by contrast, had a full complement (and more) of moral courage and was quite willing to take risks–perhaps too willing, since he had a tendency (at first, at least) to underestimate the enemy. He never complained, as McClellan did incessantly, that the government was failing to support him, but went ahead and did the job with the resources he had. Lincoln appreciated this, and after checking in to the reports of Grant’s drunkenness he concluded that they were grossly exaggerated if not made up out of whole cloth, and resisted the pressure to remove Grant. Grant was willing to fight, to take the war to the enemy, and McClellan was not. That is why Lincoln said that in 1863 that “Grant is my man, and I am his the rest of the war.”

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Britannica: Lincoln’s decision not to initiate the conflict at Fort Sumter, made at the very beginning of his administration, had important implications for the way that the war was perceived in the North. Can you describe how that decision came about and what its consequences were?

McPherson: The first problem Lincoln faced as commander in chief was what to do with the garrison at Fort Sumter. He endured a great deal of pressure from several quarters in the North to remove it in order to preserve the peace. But he was convinced that this would constitute de facto recognition of the legitimacy of the Confederacy, and in the end decided that he must make an effort to keep those soldiers at Fort Sumter in order to maintain the symbol of sovereignty.

But by April 1861 the garrison was running out of food and supplies, and the Confederates had established artillery batteries around the perimeter of Charleston harbor that could blow out of the water any attempt to supply or reinforce the fort. For Lincoln to order his navy to blast its way into the harbor with reinforcements would put the burden of having started the war on Lincoln’s shoulders. It would unite the South in support of the Confederacy (eight of the fifteen slave states had not seceded) and would divide the North. So Lincoln decided to notify the South Carolinians that he would send supplies–”food for hungry men”–and would not send reinforcements if the Confederates permitted the peaceful landing of these supplies.

This notification put the burden and stigma of starting a war on the Confederates. In effect, Lincoln flipped a coin and told Jefferson Davis “Heads I win, Tails you lose.” If the Confederates allowed the supplies to go in, the garrison of Fort Sumter with the American flag flying over the fort would maintain this important symbol of sovereignty. If they prevented the resupply of the garrison by force, they would stand convicted of firing the first shot and starting a war. The Confederate government did not hesitate: they ordered the guns to fire on Fort Sumter even before the supply ships arrived. This action united the North and placed the stigma of starting a war on the South. “Remember Fort Sumter” became a Northern slogan comparable to “Remember Pearl Harbor” for Americans in World War II.

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Britannica:Can you explain how the Emancipation Proclamation went from an aspect of strategy to a policy goal?

McPherson: The stated purpose of the Emancipation Proclamation was to free the slaves in states or parts of states that were in rebellion against the United States. Its legal justification was the power of Lincoln as commander in chief to seize enemy property being used to wage war against the United States. The slaves, whose labor supported the Confederate economy and the logistics of Confederate armies, were such property. The Emancipation Proclamation was a means to weaken the Confederacy and strengthen the Union war effort by attracting the labor power–and the military manpower–of the slave population to the Northern side. Thus it was part of the Lincoln administration’s national strategy to mobilize the resources necessary to win the war and to destroy the resources (in this case slavery) that sustained the Confederate war effort. But Lincoln also justified the Proclamation as “an act of justice” as well as a “military necessity.” It would have been a stultifying inconsistency for the North to use emancipation as a means of winning the war and restoring a Union with slavery still in that Union. Slavery in a restored Union might also sow the seeds of another war. So Lincoln became convinced that the abolition of slavery must become a goal of national policy in the war as well as an instrument of national strategy. In April 1864 the Senate, with Lincoln’s support, adopted a 13th Amendment to the Constitution abolishing slavery everywhere.

The House followed suit and passed the Amendment in January 1865, and enough states had ratified it by the end of the year for it to become part of the Constitution. Thus the Civil War became a war not only to preserve the United States as one nation, indivisible, but also to give that nation the new birth of freedom that Lincoln invoked at Gettysburg.