The general in command of the army was Winfield Scott, whose conduct of the Mexican war had made him a conspicuous military and political figure, an able officer and a most loyal Unionist, but already suffering from the infirmities of age, which soon compelled him to relinquish to younger hands the command of the army. But until after the battle of Bull Run, his was the directing mind. His immediate subordinates were Brig.-Gens. John E. Wool, also a veteran in service; William S. Harney, whose reluctance to take part in civil war soon terminated his usefulness; and David E. Twiggs, who surrendered his command to the Confederates in Texas, and going with the South, was replaced by Edwin V. Sumner. The command of the main Union force, organized from the volunteers who were pouring into Washington, devolved on Irvin McDowell, a major in the regular army, now promoted to be brigadier-general, who established his headquarters at Alexandria, across the Potomac from Washington, there directing the defence of the capital, and thence advancing to Bull Run. In this command he succeeded Gen. Joseph K. F. Mansfield. Under him, during this campaign, were many officers who rose to eminence during the war. His corps commanders at Bull Run were Gens. Daniel Tyler, David Hunter, Samuel P. Heintzelman, Theodore Runyon, and D. S. Miles; and among the brigade commanders were Gens. Erasmus D. Keyes, Robert C. Schenck, William T. Sherman, Israel B. Richardson, Andrew Porter, Ambrose E. Burnside, William B. Franklin, Oliver O. Howard, Louis Blenker, and Thomas A. Davies. Threatening the approach to Richmond from the lower Chesapeake, was Gen. Benjamin F. Butler, at Fortress Monroe. [Illustration: MAJOR-GENERAL W. B. FRANKLIN.] [Illustration: GENERAL DAVID HUNTER.] [Illustration: MAJOR-GENERAL JOSEPH K. F. MANSFIELD.] [Illustration: GENERAL GEORGE H. THOMAS.] [Illustration: GENERAL SAMUEL P. HEINTZELMAN.] Among the Confederate generals who prepared to defend Virginia, were Robert E. Lee, then in command of the Virginia State troops, Samuel Cooper, Joseph E. Johnston, P. G. T. Beauregard, James Longstreet, Jubal A. Early, Richard S. Ewell, Thomas J. ("Stonewall") Jackson, Robert S. Garnett, John C. Pegram, Benjamin Huger, John B. Magruder, and others.