March 21 began much as the previous day ended, with both sides engaging in light skirmishing. Late in the morning, Maj. Gen. Joseph A. Mower, a division commander in the XVII Corps received permission from his immediate superior, Maj. Gen. Frank Blair to launch a reconnaissance in force around the Union right. Mower took along two thirds of his division, maneuvering them into a position directly across from the Confederate left. This thinly held section of the line was manned by Brig. Gen. Evander Law’s cavalry. Sending his men forward, Mower’s infantry quickly overwhelmed the enemy cavalry and the Rebel line collapsed.
Overrunning Johnston’s own headquarters, elements of the division entered the village of Bentonville and threatened to capture the Mill Creek Bridge, the Confederates’ only line of retreat. Exasperated that Mower had escalated the fighting, Sherman ordered him to return to the Union position. At the same time, the Confederates began to counterattack. Pressing Mower back on three sides, the aggressive Mower was forced to withdraw. Realizing the vulnerability of his line, Johnston began his retreat across Mill Creek late in the evening, effectively bringing to an end the largest Civil War battle fought in North Carolina.