But Banks did not wait for Jackson. In face of the fact that his 19,000 men at Harrisonburg outnumbered the whole of Jackson's widely scattered forces, Banks retreated northward down the Valley as soon as Jackson began his campaign. On the first of May he evacuated Harrisonburg and slowly retired to Newmarket. There he lost more than half his force by the detachment of Shields with 11,000 men, who moved on May 12, by way of Luray and Front Royal to join the force at Fredericksburg, thus emphasizing that threat to Richmond which it was Jackson's function to divert.
So far Jackson's strategy was unsuccessful. He had defeated Schenck and Milroy. He had prevented a junction of their forces with those of Banks; but he had not prevented Banks from sending 11,000 men and a proportionate number of guns to strengthen the column at Fredericksburg which was intended to join McClellan before Richmond and to render him irresistible.
From Newmarket Banks continued his retreat down the valley—northward—until he rested at Strasburg and Front Royal.
In the meanwhile the administration at Washington, nervously and even absurdly apprehensive as it was, plucked up courage enough to order McDowell, with the army at Fredericksburg, reinforced by Shields with 11,000 men, to march on the twenty-sixth across country by way of the Richmond and Fredericksburg railroad, and join McClellan's right wing before Richmond.
Timidity itself could not have hesitated to consent to this movement. It placed an army of more than 40,000 men in front of Washington and between that capital and the Confederate forces of 60,000 men or less, that McClellan was already beleaguering at Richmond with 120,000 men, while it left Banks in the Valley with 8,000 and the easy support of Fremont's 15,000 men to check any movement that Jackson might make upon Washington with his force of not more than 15,000 or 16,000.
Yet so great was the apprehension felt at Washington for the safety of that city that when the time came, Lee played upon it with success and by his play upon it deprived McClellan of reinforcements from McDowell, Banks and Fremont, aggregating nearly 65,000 men.
Turning about, after his pursuit of Schenck, Jackson quickly formed a junction of his own force with Ewell's, and with 16,000 or 17,000 men turned upon Banks, who was now retreating down the Valley toward Strasburg. He struck first at a detachment at Front Royal which he surprised and almost completely destroyed on the twenty-third of May.
On the twenty-fourth Banks decided to abandon Strasburg and retreat to Winchester, destroying his stores and such wagons of his train as he could not save from capture. Jackson's cavalry destroyed a multitude more of them on march, throwing the Federal trains into the utmost confusion. Jackson now had a much stronger force than Banks—about three men indeed to Banks's one.
With his vastly superior force Jackson set out to obey his orders, which were to "clear the valley and threaten Washington," so as to compel the diversion of McDowell's army from McClellan's reinforcement before Richmond.
The task was an inviting one and Jackson accomplished it promptly. Marching tirelessly, by night as well as by day, he quickly drove Banks from Strasburg to Middletown and from Middletown to Winchester. At Winchester he broke Banks's force into bits in a hotly contested battle, and having cut off the Federal general's retreat to Harper's Ferry, sent him flying in confusion by way of Martinsburg to Williamsport on the upper Potomac. Banks fought stubbornly against such odds as no commander could hope to overcome, but finding himself beaten and his columns disintegrated he skilfully retreated over the space of thirty-four miles in a single day, and successfully placed himself behind the Potomac where his force could threaten Jackson's flank, if the great Confederate should move upon Washington by way of Harper's Ferry.