Chickamauga and Chattanooga and the Union blockade

 After confederate forces retreated to Chickamauga, the union seized control of Chattanooga. The union decided to confront the rebels at Chickamauga, the first real battle of the civil war in Georgia. The union was repelled, but at a steep price of about 20,000 casualties, a high number for the less populous southern army. The confederate general decided to rest up his exhausted and demoralized troops before pouncing on the union. The union retreated to Chattanooga where it was blockaded until Grant was able to open up a supply line. After this, Chattanooga became a foothold and a supply line for union armies in Georgia. The union also decided to blockade Georgia's, and the rest of the confederacy's, coast line. This was so the southern armies couldn't receive much needed supplies for the war.

http://en.wikipedia.org/wiki/Battle_of_Chickamauga