Grant had not commanded directly in the…

Grant had not commanded directly in the Corinth campaign.

Halleck had reorganized his army, giving Grant the powerless position of second-in-command and shuffling divisions from the three armies into three "wings".

When Halleck moves east to replace McClellan as general-in-chief, Grant resumes his field command, now named the District of West Tennessee, but before he leaves, Halleck disperses his forces, sending Buell towards Chattanooga, Sherman to Memphis, one division to Arkansas, and Rosecrans to hold a covering position around Corinth.

Part of Halleck's reason for this is that Lincoln desires to capture eastern Tennessee and protect the Unionists in the region.