So small was the military establishment of the States that in case of any future war, the army, as in Mexico, would be largely composed of volunteers; and, despite the high intelligence and warlike enthusiasm of the citizen battalions, it was evident that they were far less reliable than the regulars.  Even General Grant, partial as he was to the volunteers, admitted the superiority conferred by drill, discipline, and highly trained officers.  “A better army,” he wrote, “man for man, probably never faced an enemy than the one commanded by General Taylor in the earlier engagements of the Mexican war."* (* Grant’s Memoirs volume 1 page 168.) These troops were all regulars, and they were those who carried Scott in triumph from the shores of the Gulf to the palace of Santa Anna.  The volunteers had proved themselves exceedingly liable to panic.  Their superior intelligence had not enabled them to master the instincts of human nature, and, although they had behaved well in camp and on the march, in battle their discipline had fallen to pieces.* (* Ripley’s History of the Mexican War volume 2 page 73 etc.) It could hardly be otherwise.  Men without ingrained habits of obedience, who have not been trained to subordinate their will to another’s, cannot be expected to render implicit obedience in moments of danger and excitement; nor can they be expected, under such circumstances, to follow officers in whom they can have but little confidence.  The ideal of battle is a combined effort, directed by a trained leader.  Unless troops are thoroughly well disciplined such effort is impossible; the leaders are ignored, and the spasmodic action of the individual is substituted for the concentrated pressure of the mass.  The cavalry which dissolves into a mob before it strikes the enemy but seldom attains success; and infantry out of hand is hardly more effective.  In the Mexican campaign the volunteers, although on many occasions they behaved with admirable courage, continually broke loose from control under the fire of the enemy.  As individuals they fought well; as organised bodies, capable of manoeuvring under fire and of combined effort, they proved to be comparatively worthless.

So Jackson, observant as he was, gained on Mexican battle-fields some knowledge of the shortcomings inherent in half-trained troops.  And this was not all.  The expedition had demanded the services of nearly every officer in the army of the United States, and in the toils of the march, in the close companionship of the camp, in the excitement of battle, the shrewder spirits probed the characters of their comrades to the quick.  In the history of the Civil War there are few things more remarkable than the use which was made of the knowledge thus acquired.  The clue to many an enterprise, daring even to foolhardiness, is to be found in this.  A leader so intimately acquainted with the character of his opponent as to be able to predict with certainty what he will do