Question: The 2nd Army Corps took part in the Battle of Tannenberg,  fought between Russia and Germany from 26–30 August 1914, during the first month of what war?

Context articles: 2nd Army (Russian Empire)
Milutin Nedić
2nd Royal Bavarian Division
Battle of Charleroi
VI Corps (United States)
Battle of Tannenberg
1st Army Corps (Russian Empire)
62nd Army (Soviet Union)
52nd Army (Soviet Union)
2nd Army Corps (Russian Empire)

The Russian 2nd Army (2-я армия, "2А") was an army-level command of the Imperial Russian Army in World War I.
 It was formed just prior to the outbreak of hostilities from the units of Warsaw Military District and was mobilized in August 1914.
 The army was effectively destroyed at Battle of Tannenberg in August 1914.
 However, it was rebuilt soon thereafter and fought until almost the end of the war.
Milutin Nedić (Serbian Cyrillic: ; 26 October 1882 – 1945) was a general and Chief of the General Staff of the Royal Yugoslav Army prior to the outbreak of World War II.
 He was replaced in late 1938, and later commanded the 2nd Army Group during the German-led Axis invasion of Yugoslavia of April 1941 during World War II.
 Nedić's command consisted of General Milan Rađenković's 1st Army, responsible for the area between the Danube and the Tisza, and the 2nd Army of General Dragoslav Miljković, responsible for the border from Slatina to the Danube.
 Nedić had no Army Group reserve, but the 2nd Army was to constitute a reserve of one infantry division deployed south of Slavonski Brod.
The 2nd Royal Bavarian Division was a unit of the Royal Bavarian Army which served alongside the Prussian Army as part of the Imperial German Army.
 The division was formed on November 27, 1815, as the Infantry Division of the Munich General Command ("Infanterie-Division des Generalkommandos München.")
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 It was called the 2nd Army Division between 1822 and 1848, again between 1851 and 1859, and again from 1869 to 1872.
 It was called the 2nd Infantry Division from 1848 to 1851 (as well as during wartime) and was named the Augsburg General Command from 1859 to 1869.
 From April 1, 1872, until mobilization for World War I, it was the 2nd Division.
 In Bavarian sources, it was not generally referred to as a "Royal Bavarian" division, as this was considered self-evident, but outside Bavaria, this designation was used for it, and other Bavarian units, to distinguish them from similarly numbered Prussian units.
 The division was headquartered in Ingolstadt from 1815 to 1817, in Regensburg from 1817 to 1822, and in Augsburg from 1822 to 1919, except for the period 1871-1873, when it was part of the German occupation forces in France.
 The division was part of the I Royal Bavarian Army Corps.
The Battle of Charleroi (French: "Bataille de Charleroi" ), or the Battle of the Sambre, was fought on 21 August 1914, by the French Fifth Army and the German 2nd and 3rd armies, during the Battle of the Frontiers.
 The French were planning an attack across the Sambre River, when the Germans attacked first, forced back the French from the river and nearly cut off the French retreat by crossing the Meuse around Dinant and getting behind the French right flank.
 The French were saved by a counter-attack at Dinant and the re-direction of the 3rd Army to the north-west in support of the 2nd Army, rather than south-west.
The VI Corps was activated as VI Army Corps in August 1918 at Neufchâteau, France, serving in the Lorraine Campaign.
 Constituted in the Organized Reserves in 1921, it was allotted to the Regular Army in 1933 and activated on 1 August 1940 at Fort Sheridan, Illinois.
 VI Corps took part in some of the most high-profile operations in World War II.
The Battle of Tannenberg was fought between Russia and Germany from 26–30 August 1914, during the first month of World War I.
 The battle resulted in the almost complete destruction of the Russian Second Army and the suicide of its commanding general, Alexander Samsonov.
 A series of follow-up battles (First Masurian Lakes) destroyed most of the First Army as well and kept the Russians off balance until the spring of 1915.
 The battle is particularly notable for fast rail movements by the Germans, enabling them to concentrate against each of the two Russian armies in turn, and also for the failure of the Russians to encode their radio messages.
 It brought considerable prestige to Field Marshal Paul von Hindenburg and his rising staff-officer Erich Ludendorff.
The 1st Army Corps (Russian: 1-й армейский корпус ) was a formation in the Imperial Russian Army, formed in the 1870s.
 It took part in the Russo-Turkish War of 1877—78, and later, in August 1914, the 1st Army Corps fought as part of the Second Army in the Battle of Tannenberg.
 There, it was defeated by the Germans along with the rest of the Second Army.
 During the rest of World War I, it took part in other operations, up until around 1918.
The 7th Reserve Army was formed 28 May 1942 as part of the Stavka Reserve (RVGK).
 Within one month, this force had been redesignated the 62nd Army.
 From mid August 1942 until late January 1943, the 62nd Army, under the command of General Vasily Chuikov, fought in the Battle of Stalingrad.
 62nd Army conducted an epic defense of the city against repeated and desperate attacks by the German 6th Army.
 The Army, along with the 64th Army, was operating under the Soviet Stalingrad Front.
 After the German assault at Stalingrad had come to utter disaster, the 62nd Army was uniquely awarded the Order of Lenin, and granted Guards status as the 8th Guards Army.
It was created on 25 August 1941 from the headquarters of the 25th Rifle Corps and defended north of Novgorod.
 On 26 September 1941, the 52nd Army headquarters was used to form the 4th Army (II Formation).
 The 52nd Army headquarters was reestablished on 28 September 1941.
 In May 1943, the army was moved to control of the Reserve of the Supreme High Command ("Stavka" Reserve).
 "Stavka" released the 52nd Army to subordination of the Steppe Front in July 1943, and the 52nd Army thereafter fought in the Ukraine, southern Poland, southeastern Germany, and finally in northern Czechoslovakia.
The 2nd Army Corps (Russian: 2-й армейский корпус ) was a formation in the Imperial Russian Army that was active during World War I.
 It was headquartered in Grodno prior to the outbreak of the war, and took part in the Battle of Tannenberg in August 1914.