The year 1861 had been devoted rather to preparation for war than to war itself; for every day brought home to the North the certainty that the struggle would be tremendous--that large armies must fight over thousands of miles--and that to conquer, men must go forth not by thousands, but by hundreds of thousands, and endure such privations, such extremes of climate, as are little known in European warfare. But by the 1st Dec., 1861, 640,000 had been enrolled. The leading features of the plan of war were an entire blockade of the rebel coast, the military control of the border Slave States, the recovery of the Mississippi river, which is the key of the continent, and, finally, the destruction of the rebel army in Virginia, which continually threatened the North, and the conquest of Richmond, the rebel capital. General M‘Clellan had in the army of the Potomac, which occupied Washington and adjacent places, more than 200,000 men, well armed and disciplined. In Kentucky, General Buell had over 100,000. The rebel force opposed to General M‘Clellan was estimated at 175,000, but is now known to have been much less. General M‘Clellan made little use of the spy-service, and apparently cared very little to know what was going on in the enemy’s camp--an indifference which before long led him into several extraordinary and ridiculous blunders. As Commander-in-Chief, General M‘Clellan had control over Halleck, Commander of the Department of the West, while General Burnside commanded in North Carolina, and Sherman in South Carolina.