Disunion follows the Civil War as it unfolded.

On Aug. 3, 1862, Gen. George B. McClellan received orders to begin withdrawing the Army of the Potomac from its position in front of Richmond, Va. The new Union general in chief, Henry Halleck, had given McClellan a choice: to renew his offensive against Richmond or ship his army back to Washington. McClellan resented and resisted Halleck’s authority, and stubbornly refused to advance, thinking Halleck would eventually recognize the folly of a withdrawal.

And folly it was, McClellan’s obstinacy and lack of battlefield success notwithstanding. Once McClellan’s troops were in transit, half the Union forces in the Virginia theater were out of action. With the threat to Richmond removed, Gen. Robert E. Lee was free to stage a bold counter-offensive into northern Virginia, which would lead to the near destruction of the Union Army under General John Pope at the Second Battle of Bull Run, the invasion of Maryland, the bloody Battle of Antietam and the Confederacy’s best chance to win the war outright.

The root of this tactical blunder was the radical and absolutely necessary transformation of Federal strategy initiated by President Abraham Lincoln in July 1862. At the start of the war, he had hoped that aggressive military action, coupled with a “conciliatory” policy on slavery, would induce the South to negotiate a return to the Union in short order. But a year of costly fighting had proved that the Confederacy’s military strength and political will could not be overcome without a far longer and more destructive war. By the summer of 1862, the situation was clear: Union troop strength had to be greatly increased – Lincoln was asking for 300,000 new volunteers – and offensives had to be pressed with greater energy.

But Lincoln had also concluded that the elimination of slavery must become a Federal war aim. He had always believed slavery was morally wrong and incompatible with democracy. It was the motive for secession and the basis of the South’s economic and military strength. So long as slavery existed it would remain a source of conflict between the states. Lincoln concluded that the longer, costlier war for the Union that now seemed necessary could be justified only if it removed the root cause of conflict.

To carry out such a strategy he needed a general whose determination and commitment matched his own. What he had instead was General McClellan, who was both a balky and reluctant field commander and the symbolic champion of the opposition Democratic Party. On July 8, 1862, he met with McClellan at the general’s headquarters, to see whether he was able and willing to fight the long war.

McClellan was a highly respected West Point professional, who had been put in command of the Army immediately after the disaster at Bull Run in July 1861. For the first months of his tenure he received universal acclaim, and was given a free hand in organizing the Federal armies. But the accolades went to his head: he believed the outpouring of public support he enjoyed during his first six months in command was a kind of symbolic election, which gave him moral authority comparable to the president’s. Although he saw himself as a disinterested military professional, he was in fact a partisan Democrat “of the Stephen A. Douglas school,” who maintained close contact with the leaders of the Democratic Party and pressed Lincoln to adopt the “conservative” policies favored by his party.

Library of Congress

He thought antislavery Republicans were just as responsible as secessionists for the outbreak of war, and that if he was to restore the Union he had to defeat both the Southern armies on his front and the Radical Republicans who would stab him in the back. He even flirted with idea of a Congressionally sanctioned “dictatorship,” which would give him control of war policy, leaving Lincoln as a figurehead. From the start of his tenure he had waged a series of political and bureaucratic battles, trying to make himself the dominant voice in the president’s councils. “I have no choice,” he told his wife. “The people call upon me to save the country – I must save it & cannot respect anything that stands in the way.”

His illusions flourished in the hothouse of his headquarters, where he was surrounded by loyalists who mirrored and even exaggerated his moods. He saw himself as the agent of Divine Providence, chosen by God to save the Republic – and visit judgment on his enemies. Even his defeat by Lee in the Seven Days battles was a sign that God was on his side. “I think I begin to see His wise purpose in all this,” He wrote his wife on July 10. “If I had succeeded in taking Richmond now the fanatics of the North might have been too powerful & reunion impossible.”

Most dangerously, McClellan was utterly contemptuous of Abraham Lincoln’s character, intelligence, social origins and morals. He dismissed the president as “the original Gorilla,” a well-meaning but weak-minded “baboon” surrounded by fools and traitors. He believed that his July 8 meeting was his opportunity to impress his will and his ideas on the president.

Related Disunion Highlights Explore multimedia from the series and navigate through past posts, as well as photos and articles from the Times archive. See the Highlights »

They met on the deck of Lincoln’s steamer, where a canvas awning shaded them from the day’s insufferable heat. Lincoln asked McClellan when he planned to resume the offensive. Instead of answering, McClellan begged leave to submit a letter detailing his views, which he handed the president. Instead of taking it and leaving, Lincoln read it right there. But if its contents astonished him he gave no sign.

The letter said nothing about the Army’s defeat, nor did it propose a plan for renewing the offensive. It was instead a political manifesto, laying out McClellan’s grand design for the future civil and military policy of the country. McClellan demanded a “conservative” approach to three basic policies: the legal consequences of secession, the status of slavery and the division of power between civil and military authorities. He denied the basic premise of Lincoln’s policy, that secession was an act of rebellion. Instead, he declared that the government had no right to “subjugate” the seceded states. So when their districts were occupied by Union forces, the “political rights” of Southerners must be automatically restored. As McClellan well knew, such a policy would slowly restore the Democratic Party’s national majority.

McClellan also warned that “A declaration of radical views, upon slavery, will rapidly disintegrate our present Armies.” Coming from the commander of the nation’s most powerful army, which was imbued with his cult of personal loyalty, that warning had threatening implications. Finally, McClellan wanted Lincoln to delegate control of all war-related policy to “a Commander in Chief of the Army; one who possesses your confidence, understands your views and who is competent to execute your orders.” McClellan was clearly nominating himself for the post.

In effect, McClellan was demanding that Lincoln abandon the responsibilities of his office and the platform of his party, and turn power over to the general who had just lost the war’s greatest battle at the time.

Lincoln pocketed the letter and kept his poker face, but the meeting had crystallized his strategic ideas. In the two weeks that followed he made a series of decisions which radically transformed Federal strategy. On July 11 he ordered Gen. Henry Halleck, commander of Federal armies in the West, to assume command, under the president, of all Federal armies — thus making him McClellan’s superior.

Then, on July 12, in a private conversation with Secretary of State William Seward and Navy Secretary Gideon Welles, Lincoln declared his intention to issue an emancipation proclamation, freeing all slaves in the rebellious states; and on July 22 he presented a draft proclamation to an astonished cabinet. He acted with full awareness that such a proclamation would end all hope of conciliation and commit the Union to an all-out war.

First, however, he had to deal with McClellan. Indeed, Halleck’s first task would be to force General McClellan to resume the offensive — but McClellan was immovable, confident that his popular prestige and political support gave him sovereign immunity. On July 11, the very day of Halleck’s appointment, he boasted to his wife, “I have commenced receiving letters from the North urging me to march on Washington & assume the Govt!!”

Fearful of removing him outright, Halleck and Lincoln chose the half-measure of shipping McClellan’s Army north without him. They thus set the stage of Lee’s invasion of Maryland, and McClellan’s return to command for the Antietam campaign.

Follow Disunion at twitter.com/NYTcivilwar or join us on Facebook.

Sources: Eric Foner, “The Fiery Trial”; George B. McClellan, “Civil War Papers,” ed. by Stephen W. Sears; James M. McPherson, “Tried By War”; Ethan S. Rafuse, “McClellan’s War”; Stephen W. Sears, “George B. McClellan.”

Richard Slotkin is Olin professor of American Studies emeritus at Wesleyan University and author of “The Long Road to Antietam: How the Civil War Became a Revolution.”