 Complete the following phrase:  The mountainous, largely Unionist region of East Tennessee was considered by President Abraham Lincoln to be a key war objective. Besides possessing a population largely loyal to the Union, the region was rich in grain and livestock and controlled the railroad corridor from Chattanooga to Virginia. Throughout 1862 and 1863, Lincoln pressured a series of commanders to move through the difficult terrain and occupy the area. Ambrose Burnside, who had been soundly defeated at the Battle of Fredericksburg in December 1862, was transferred to the Western Theater and given command of the Department and the Army of the Ohio in March 1863. Burnside was ordered to move against Knoxville as swiftly as possible while, at the same time, Maj. Gen. William S. Rosecranss Army of the Cumberland was ordered to operate against Bragg in Middle Tennessee the Tullahoma campaign and the subsequent 