After the Union capture of Fort Henry and Fort Donelson in February, Confederate General Albert Sidney Johnston withdrew his forces from central Tennessee to reorganize. As part of this withdrawal, Johnston evacuated Nashville on February 23, surrendering this important industrial center to Union Brig. Gen. Don Carlos Buell's Department of the Ohio army and making it the first Confederate state capital to fall to the Union. After taking Nashville, Buell showed little inclination for further offensive operations, especially towards the pro-Union region of East Tennessee. On March 11, Buell's army was merged into the new Department of the Mississippi under General Henry Halleck. In late March, Halleck ordered Buell southwest to reinforce Grant's army near Pittsburgh Landing on the Tennessee River. Buell departed, leaving a 7,000-man garrison in Nashville along with Maj. Gen. Ormsby Mitchel's 10,000-man 3rd Division. Mitchel had earlier assisted in the capture of Nashville and accepted the surrender of the city. With the withdrawal of both Confederate and Union forces towards western Tennessee, central Tennessee became an economy of force operation. Facing minimal Confederate resistance, Mitchel moved his division southeast out of Nashville on March 18 towards Murfreesboro, arriving on March 20.