Because his army lacked the strength to assault Washington, General Lee had decided on September 3 to invade Maryland. North of the Potomac his army would be a constant threat to Washington. This would keep Federal forces out of Virginia, allowing that ravaged land to recuperate from the campaigning that had stripped it. It would give Maryland’s people, many of whom sympathized with the South, a chance to throw off the Northern yoke. From Maryland, Lee could march into Pennsylvania, disrupting the east-west rail communications of the North, carrying the brunt of war into that rich land, drawing on its wealth to refit his army. [Illustration: _Lee’s army crossing the Potomac; Union scouts in foreground._ From wartime sketch by A. R. Waud. Courtesy, Library of Congress.] [Illustration: LEE INVADES MARYLAND] Larger political possibilities loomed, too. The North was war weary. If, in the heartland of the Union, Lee could inflict a serious defeat on Northern arms, the Confederacy might hope for more than military dividends—the result might be a negotiated peace on the basis of Southern independence. Too, a successful campaign might induce England and France to recognize the Confederacy and to intervene for the purpose of mediating the conflict. So it was that the hopes of the South rode with this Army of Northern Virginia as it marched into Frederick, Md., on September 7. _McClellan in Command_ On that same September 7, another army assembled at Rockville, Md., just northwest of Washington. Soon to be nearly 90,000 strong, this was Maj. Gen. George B. McClellan’s Army of the Potomac. Its goal: To stay between Lee’s army and Washington, to seek out the Confederate force, and, as President Abraham Lincoln hoped, to destroy it. Hastily thrown together to meet the challenge of Lee’s invasion, this Union army was a conglomerate of all the forces in the Washington vicinity. Some of its men were fresh from the recruiting depots—they lacked training and were deficient in arms. Others had just returned from the Peninsular Campaign where Lee’s army had driven them from the gates of Richmond in the Seven Days’ Battles, June 26-July 2. Still others were the remnants of the force so decisively beaten at Second Manassas. [Illustration: _Gen. Robert E. Lee._ From photograph by Julian Vannerson. Courtesy, Library of Congress.] [Illustration: _Maj. Gen. George B. McClellan._ From photograph by Matthew B. Brady or assistant. Courtesy, National Archives.] In McClellan the Union army had a commander who was skilled at organization. This was the reason President Lincoln and Commander in Chief of the Army Henry Halleck had chosen him for command on September 3. In 4 days he had pulled together this new army and had gotten it on the march. It was a remarkable achievement.