Army of the Ohio in Southern Victory
The Army of the Ohio had been formed in 1861 at the start of the War of Secession. Although it had been the most successful army the Union fielded, its efforts were ultimately overshadowed by the North's defeat in the East.
When the Second Mexican War began in 1881, the Army of Ohio was reformed. It was the largest army fielded by any side during the conflict. After the Army of the Potomac was defeated in it's flanking attempt at Winchester, the Army of Ohio became the main focus of the war. All major reinforcements were channeled there as Brigadier General Orlando Willcox launched an invasion of Kentucky with the aim of returning that state to the union.
The army was 50,000 strong, consisting of Regular soldiers and volunteers, many of whom did not mix very well. The situation was made worse by their commander's poor planning. Willcox was slow to move, blatantly advertised his intentions and all but telegraphed his opposite number ahead of time. When the blow finally came, the Army crossed the Ohio River and attacked the city of Louisville, head on, beginning the bloodiest campaign of the war. The attack quickly bogged down as the army found itself fighting house to house, and street to street. This tactic chew up men greatly and ate at the army's morale.
After a cease fire was called and terms rejected, the army received reinforcements, and attempted a flanking manoeuvre while feinting an attack in the city. However, defensive works that had been built on the city's flanks slowed the offensive down, and thanks in part to a series of holding actions organized by Second Lt. Jeb Stuart Jr., the Confederates were able to rush reinforcements to stop the army's advance, resulting in both sides digging in and trench warfare.
As the war elsewhere began to turn against the US, the Army of Kentucky launched an attack against the Army of the Ohio's western flank, successfully routing them and forcing them back across the river.