Wherein corps and cracks are formed
..................................................................................................................................
After the Two Weeks That Changed The War the two Armies of the Potomac began moving. Ron over at All Not So Quiet Along the Potomac has done some great stuff about the Confederate preparation and subsequent departure from Northern Virginia, which I will not attempt to duplicate, so make sure you stop over and read it.
On March 8, 1862, Abraham Lincoln and his new Secretary of War, Edwin Stanton, made a momentous decision--they would overrule McClellan's armies and establish four corps d'armee. French for "body of the army", the grouping of divisions in "corps" had been popularized by the phenomenal success of Napoleon. The units were designed to be armies fully capable of operating independently, but which worked in conjunction within the same theater. But since the 14 divisions of the Army of the Potomac were each larger than any American army previously in existence, the idea was anathema to many Northern leaders.
As usual, the general-in-chief, Maj. General George B. McClellan, lay at the center of what had become a controversial discussion fueled by the Joint Committee for the Conduct of the War. In McClellan's earliest days in Washington, he had stated his intention to form his army into corps. But as part of his systematic effort to remake the U.S. Army in his own image, he had held off on grouping the divisions into corps without explanation. In the meantime, the Joint Committee had caught corps fever, and on February 25 at 8:00 pm, had met with Lincoln in the White House to urge their creation. According to the Committee's report published in 1863:
They made known to the President that, having examined many of the highest military officers of the army, their statements of the necessity of dividing the great army of the Potomac into corps d'armie [sic] had impressed the committee with the belief that it was essential that such a division of that army should be made...The President observed that he had never considered the organization of this army into army corps so essential as the committee seemed to represent it to be; still he had long been in favor of such an organization. General McClellan, however, did not seem to think it so essential, though he had at times expressed himself as favorable to it. The committee informed the President that the Secretary of War had authorized them to say to him that he deemed such an organization necessary.

