Having thus eluded his pursuers, Banks and Saxton, Jackson pushed his foot cavalry into Strasburg in advance of both Fremont and Shields, though each of them had had a much shorter line of march than his own in order to reach that place. He had shaken off Banks and Saxton for a time at least, but he had pushed his small force in between Fremont's equal army on the one hand and Shields's superior one, which was now supported by additional troops under McDowell's own command, on the other. His problem was to prevent the junction of these two armies sent to crush him, to escape them and—if possible—to defeat them separately. One of these armies outnumbered his own in the proportion of four men to three while the other equaled his force. But if he could keep them separated and attack them in positions of his own choosing, where they could not both fight him at once, he did not despair of beating them.
McDowell, reckoning upon the easy superiority of his force, sent detachments hither and yon, to "head off" Jackson, and prevent his escape, that seeming now to be the only thing to be done with a fleeing general whose army was beset on every side, outnumbered, and hopelessly entangled.
In execution of these orders a whole day was wasted by Shields, through mistakes as to routes, and Jackson slipped out of Strasburg on his way to Harrisonburg, Cross Keys and Port Republic, points at which he planned to turn upon his enemy and fight him in detail.
By the burning of bridges and the adroit disposition of troops in a region broken by mountain ranges and laced by streams at that time of year unfordable, Jackson managed to keep the divisions of his adversary separated as they severally pursued his retreat, intent upon capturing or destroying him.
So greatly overwhelming were the Federal numbers that General Shields urgently protested to General McDowell against the sending of any more men to his assistance. Says General McDowell in an official utterance:
He [Shields] had been in that country before and his command had suffered somewhat. He wrote me a letter stating his apprehensions, saying that if troops instead of supplies kept coming over, the troops would starve, and asking why I should bring so many there; that he had enough men to clear the Valley out and for God's sake not to send him any more men.
McDowell reassured Shields as to the abundance of supplies and that commander, with his superabundance of men, cheerfully undertook the task of "clearing out the Valley" which seemed to him easy. He had not adequately reckoned upon the genius of Stonewall Jackson—that was all.
The "foot cavalry" had now retreated with splendid success, as far as Jackson intended that they should. He was pursued by the two armies, but he had succeeded in keeping them separated by an unfordable river, while divesting himself of his embarrassing supply train and his still more embarrassing company of Federal prisoners. These, together with his own sick and wounded, he had sent under escort to Staunton.
Thus, stripped for action, he turned upon his pursuers to rend them. Fremont's force and that under Shields were separated by a river. Jackson had destroyed every bridge that crossed that stream except the one at Port Republic, which he securely held for his own use in the contemplated operations. He had about 13,000 men of all arms available for battle uses. Fremont, who was hotly pursuing him, had about 11,500, while Shields's force—weakened by detachments—marching down the other side of the river, was much smaller, not over three or four thousand effectives. Exact figures are unattainable.
Jackson had effectually prevented the union of these two armies. He decided to fight them now, one at a time.