As far as Union General George B. McClellan was concerned he had saved the Union at the Battle of Antietam. With Maryland now safe from invasion, McClellan wanted two things. One was the removal of Secretary of War, Edwin Stanton and the removal of Henry Halleck as general in chief. McClellan wanted to be in charge of the Union's entire war effort. He wanted control of the war without presidential or congressional interference. He believed that meeting of governors of the Northern states sponsored by Pennsylvania Governor Andrew Curtin would be the forum which would endorse McClellan's views. At this time, public support of McClellan and favorable newspaper support from such publications as Harper's Weekly, would help him achieve his goals.
On September 30, 1862, General in Chief telegraphed General McClellan that he was very pleased about the battle reports furnished by McClellan on the victory at South Mountain and Antietam. His congratulations were overwhelming and he promised to convey all of this to President Lincoln.
Major George B. McClellan received poor advice from his cavalry and from local citizens regarding the number of troops he would have to battle against at Sharpsburg, known better as the Battle of Antietam. McClellan believed that Stonewall Jackson commanded between 40 to 50,000 troops and were close to joining General Lee at Sharpsburg, who commanded 30,000 soldiers.McClellan's estimates were vastly off target. When the Battle of Antietam finally began on September 17, 1862, Lee's total number of troops were barely 39,000.
President Lincoln appointed Major General George B. McClellan to general in chief on November 1, 1861. He replaced the retiring General in Chief Winfield Scott. Lincoln relieved McClellan of his title on March 11, 1862. McClellan was not in Washington DC at this time. He was in the process of organizing the Peninsula campaign. It is written that Lincoln did not believe that McClellan could hold his position as general in chief and conduct the Peninsula campaign at the same time.
Much of General George B. McClellan's correspondence to Washington DC and personal letters are now in the public domain. A good number of historians have to the belief that McClellan had a "Calvinistic" belief in predestination. The totality of these published papers appear to demonstrate that McClellan believed that God had called him to save the Union.
In his initial plan to end the Southern rebellion, General McClellan outlined a multipronged offensive. The key area of operations would be in Virginia.
As the Union's Peninsula campaign was in its early stages, General McClellan was certain that President Lincoln was hampering McClellan's war operations. Lincoln had stepped in and retained the corps under General McDowell to defend Washington DC. Lincoln believed this was a necessity.
While the armies of General Lee and General McClellan were within striking distance on September 15, 1862, Lee sought to disguise the fact that his army was in no position to stave off an assault by the Army of the Potomac. He disguised his lack of strength by flying all the flags of his regiments from hidden positions, hoping McClellan would believe all of Lee's army was settled in at Sharpsburg. Confederate Major General Longstreet was ordered to repeatedly fire all of his artillery scattered along the Confederate lines. This made it appear that the Rebels were fully armed and ready for battle. That response from Lee, combined with McClellan's natural streak of always hesitating, allowed for more Southern troops to arrive from Harpers Ferry. By the 17th of September, Lee had all the troops he could muster and McClellan felt strong enough to launch an assault, thus beginning the fateful Battle of Antietam.
Although Major General George B. McClellan was not part of the Second Battle of Bull Run, he estimated that General Lee had 120,000 troops. This was double the actual number of troops that General Lee had at his disposal. McClellan's estimate was based on numerous rumors instead of actual facts. McClellan had consistently over estimated the number of Rebel troops that were operating in Northern Virginia.
Major General George B. McClellan was a Democrat. His plan was to become the Union's general in chief, a post held by the aging General Winfield Scott. McClellan believed that the future secretary of war, Edwin Stanton, would be his ally in the removal of Scott. Stanton was a prominent Democrat and a former member of President James Buchanan's cabinet.
General McClellan, in 1861, recommended that 20,000 troops were needed to defend Washington DC. With other troops stationed in the vicinity , additional reinforcements could be rapidly sent to the defense of the capitol.
Major General George B. McClellan was not a supporter of slavery. With that said, he did believe that the preliminary proclamation emancipation would intensify the South's commitment to the war. This was because it threatened both the property interests of slave owners and the social interest in preserving white supremacy.
Major General George B. McClellan was aware that Texas and the US Territories bordering Mexico were potential trouble spots for the US. With regards to that, McClellan recommended that the US maintain cordial relations with Mexico as a means of intelligence gathering on Confederate forces that may try to dominate US areas in the Southwest.