In March he advanced down the Valley in the direction of Winchester, and, coming upon a considerable force of the enemy at Kernstown, made a vigorous assault upon them; a heavy engagement ensued, and, though Jackson was defeated and compelled to retreat, a very large Federal force was retained in the Valley to protect that important region.

A more decisive diversion soon followed.

Jackson advanced in May upon General Banks, then at Strasburg, drove him from that point to and across the Potomac; and such was the apprehension felt at Washington, that President Lincoln ordered General McDowell, then at Fredericksburg with about forty thousand men, to send twenty thousand across the mountains to Strasburg in order to pursue or cut off Jackson.
Thus the whole Federal programme in Virginia was thrown into confusion.

General Banks, after the fight at Kernstown, was kept in the Valley.

After Jackson's second attack upon him, when General Banks was driven across the Potomac and Washington threatened, General McDowell was directed to send half his army to operate against Jackson.