FOLLOWING THE BATTLE of Chattanooga (November 23-25, 1863), Ulysses S. Grant sent forces to relieve Knoxville, where Major General Ambrose E. Burnside had been besieged by Lieutenant General James Longstreet. Although General Braxton Bragg's Army of Tennessee had left Chattanooga in disorder, the need to send troops to Knoxville prevented Grant from launching an aggressive campaign into Georgia. Longstreet raised his siege upon learning that reinforcements were on the way, but he remained a menace in east Tennessee during the customary winter slackening of military action. Grant wanted to drive Longstreet away, but problems of supply and weather frustrated his efforts. Grant finally realized that Longstreet faced the same problems and once out of Tennessee might do more damage elsewhere.
The winter months of 1864 found Grant preparing for the inevitable spring campaign in Georgia. At the same time, he could not ignore the deliberations of Congress as it considered a bill to revive the rank of lieutenant general, intending it for Grant. In January, Grant and his staff mapped out grand strategy, forwarding suggestions to Major General Henry W. Halleck.
In late February, the lieutenant general bill passed, and President Abraham Lincoln called Grant to Washington to receive his commission and assume command of all the armies. Halleck immediately resigned his post of general-in-chief and was appointed Grant's chief of staff, a move which provided the U. S. Army with a modern command system, freeing Grant to take the field while Halleck dealt with administrative matters and implemented Grant's orders.