Question: Joseph Alexander Cooper was an American soldier who commanded units at a battle fought on September 18–20, 1863 and was the first major battle of the war fought where? 

Context paragraphs:
Battle of Assaye: The Battle of Assaye was a major battle of the Second Anglo-Maratha War fought between the Maratha Empire and the British East India Company.  It occurred on 23 September 1803 near Assaye in western India where an outnumbered Indian and British force under the command of Major General Arthur Wellesley (who later became the Duke of Wellington) defeated a combined Maratha army of Daulat Scindia and the Raja of Berar.  The battle was the Duke of Wellington's first major victory and one he later described as his finest accomplishment on the battlefield.

Battle of Chickamauga: The Battle of Chickamauga, fought on September 18–20, 1863 between Union and Confederate forces in the American Civil War, marked the end of a Union offensive in southeastern Tennessee and northwestern Georgia — the Chickamauga Campaign.  It was the first major battle of the war fought in Georgia, the most significant Union defeat in the Western Theater, and involved the second-highest number of casualties after the Battle of Gettysburg.

Battle of Jutland: The Battle of Jutland (German: "Skagerrakschlacht" , the Battle of Skagerrak) was a naval battle fought by the British Royal Navy's Grand Fleet under Admiral Sir John Jellicoe, against the Imperial German Navy's High Seas Fleet under Vice-Admiral Reinhard Scheer during the First World War.  The battle unfolded in extensive maneuvering and three main engagements (the battlecruiser action, the fleet action and the night action), from 31 May to 1 June 1916, off the North Sea coast of Denmark's Jutland Peninsula.  It was the largest naval battle and the only full-scale clash of battleships in that war.  Jutland was the third fleet action between steel battleships, following the smaller but more decisive battles of the Yellow Sea (1904) and Tsushima (1905) during the Russo-Japanese War.  Jutland was the last major battle in world history fought primarily by battleships.

Battle of the Persian Border: The Battle of the Persian Border was the second encounter between the forces of Media and Persia.  Though not a decisive victory for Persia, it signaled the diminishing power of Media in Southwest Asia.  It was the first battle Cambyses I had fought in, and the first which he had fought with his son, Cyrus the Great.  The first major battle, which lasted two days, was an attempt to bring freedom to Persia.  It also prompted the Persians to retire south, and fight a third battle.  It was narrated by Nicolaus of Damascus, and among others who also mentioned the Battle of Hyrba, but Herodotus does not mention this battle.  Most historians on the battle consider Herodotus to be mentioning only the first and last battles in the war, which is partly based on the description of his two battles.  At the border this became the first major battle between the two powers.  Cyrus managed to escape the enemy without retreating, thus ending the battle and prolonging the struggle without a complete victory for Astyages, the king of the Medes.  The next battle became the last stand for the Persians; as their very existence relied on the outcome of the war, which had to be won.

Battle of Peachtree Creek: The Battle of Peachtree Creek was fought in Georgia on July 20, 1864, as part of the Atlanta Campaign in the American Civil War.  It was the first major attack by Lt. Gen. John Bell Hood since taking command of the Confederate Army of Tennessee.  The attack was against Maj. Gen. William T. Sherman's Union army which was perched on the doorstep of Atlanta.  The main armies in the conflict were the Union Army of the Cumberland, commanded by Maj. Gen. George Henry Thomas, and two corps of the Confederate Army of Tennessee, commanded by Lt. Gen. John B. Hood.  The battle of Peachtree Creek was the first battle fought by Hood as commander of the Army of Tennessee.

Joseph Alexander Cooper: Joseph Alexander Cooper (November 25, 1823 – May 20, 1910) was an American farmer, soldier, and civil servant.  A Southern Unionist, he fought for the Union Army during the American Civil War, commanding units at Mill Springs, Stones River, Chickamauga, Franklin, Nashville, Bentonville, and in the Knoxville and Atlanta campaigns.  He had achieved the rank of Brevet Major General by the time he was mustered out in early 1866.

Battle of Mount Lycaeum: The Battle of Mount Lycaeum was a battle fought between Sparta led by Cleomenes III and the Achaean League commanded by Aratus.  It was the first major battle of the Cleomenean War.  The battle occurred at Mount Lycaeum on the border of Elis and Arcadia and ended in a Spartan victory.

Battle of the Lys (1940): The Battle of the Lys (French: "Bataille de la Lys" , Dutch: "Leieslag" ) was a major battle between Belgian and German forces during the German Invasion of Belgium of 1940 and the final major battle fought by Belgian troops before their surrender on 28 May.  It was the bloodiest of the 18 Days' Campaign.  The battle was named after the river Leie (known as the Lys in French), where the battlefield was situated.

Battle of Boquerón (1932): The Battle of Boquerón was a battle fought from September 7-29, 1932, between the Bolivian and Paraguayan armies in and around the stronghold of Boquerón.  It was the first major battle of the Chaco War.  The outpost ("fortín") of Boquerón, among others, had been occupied by Bolivian troops since late July 1932 following instructions of president Daniel Salamanca, which led to the escalation of what began as a border conflict into a full-scale war.

Battle of Pima Butte: The Battle of Pima Butte, or the Battle of Maricopa Wells, was fought on September 1, 1857 at Pima Butte, Arizona near Maricopa Wells in the Sierra Estrella.  Yuma, Mohave, Apache and Yavapai warriors attacked a Maricopa village named Secate in one of the largest battles in Arizona's history.  It was also the last major battle fought by the Yumas and the last major battle fought solely between native Americans in North America.

Supporting paragraphs: Joseph Alexander Cooper Battle of Chickamauga
Answer: Georgia