The First Battle of nn (Turkish: Birinci nn Muharebesi) took place between 6 and 11 January 1921 near nn in Hdavendigr Vilayet (present-day Eskiehir Province, Turkey) during the Greco-Turkish War (191922), also known as the western front of the larger Turkish War of Independence. This was the first battle for the Army of the Grand National Assembly that was newly built standing army (Dzenli ordu) in place of irregular troops.

The Greco-Turkish War of 1919–1922 was fought between Greece and the Turkish National Movement during the partitioning of the Ottoman Empire in the aftermath of World War I, between May 1919 and October 1922.

The Greek campaign was launched primarily because the western Allies, particularly British Prime Minister David Lloyd George, had promised Greece territorial gains at the expense of the Ottoman Empire, recently defeated in World War I, as Anatolia had been part of Ancient Greece and the Byzantine Empire before the Ottomans captured the area. The armed conflict started when the Greek forces landed in Smyrna (now İzmir), on 15 May 1919. They advanced inland and took control of the western and northwestern part of Anatolia, including the cities of Manisa, Balıkesir, Aydın, Kütahya, Bursa and Eskişehir. Their advance was checked by Turkish forces at the Battle of Sakarya in 1921. The Greek front collapsed with the Turkish counter-attack in August 1922, and the war effectively ended with the recapture of Smyrna by Turkish forces and the great fire of Smyrna.

As a result, the Greek government accepted the demands of the Turkish National Movement and returned to its pre-war borders, thus leaving East Thrace and Western Anatolia to Turkey. The Allies abandoned the Treaty of Sèvres to negotiate a new treaty at Lausanne with the Turkish National Movement. The Treaty of Lausanne recognized the independence of the Republic of Turkey and its sovereignty over Anatolia, Istanbul, and Eastern Thrace. The Greek and Turkish governments agreed to engage in a population exchange.