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?

full_context: Document 1: III Corps (Grande Armée): The III Corps of the Grande Armée was the designation of a few military units during the Napoleonic Wars. The III Corps came to prominence between 1805 and 1809 under the command of Marshal Louis-Nicolas Davout, when it repeatedly scored impressive victories single-handedly or in conjunction with other French forces. Napoleon called it ""My tenth legion"", in reference to Julius Caesar's finest unit, the X Equestris. Then troops from that Corps took part in many battles in Poland (1807) e.g. Czarnowo, Pultusk, Golymin, Eylau, in Bavaria at Teugen-Hausen, Eckmuhl and in Austria 1809 at Wagram. These troops later were reorganized as I Corps and included French, German/Polish units. It also included the 127th to 129th ""régiment d'infanterie de ligne"" from the north German countries of Oldenburg, Bremen and Hamburg that were annexed shortly before and thus counted as French.
Document 2: Battle of Tannenberg: 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.
Document 3: August 1914 (novel): August 1914 is a Russian novel by Aleksandr Solzhenitsyn about the defeat of the Imperial Russian Army at the Battle of Tannenberg in East Prussia. The novel was completed in 1970, first published in 1971, with an English translation the following year. The novel is an unusual blend of fiction narrative and historiography, and has given rise to extensive and often bitter controversy, both from the literary as well as from the historical point of view.
Document 4: I Cavalry Corps (Grande Armée): I Cavalry Corps (Grande Armée) was a French military formation that existed during the Napoleonic Wars. For one month in 1806–1807, Emperor Napoleon split his Reserve Cavalry Corps into the I and II Cavalry Corps. At that time, Marshal Joachim Murat took command of the short-lived I Cavalry Corps before resuming leadership over Napoleon's Reserve Cavalry when the experiment ended. The I Cavalry Corps was not recreated until 1812 for the French invasion of Russia when command was exercised by Étienne Marie Antoine Champion de Nansouty. The formation fought at Borodino and Tarutino. After being destroyed during the retreat from Russia, I Cavalry Corps was reconstituted in 1813 and Marie Victor de Fay, marquis de Latour-Maubourg was appointed to lead it. The corps fought at Lutzen, Bautzen, Dresden, and Leipzig. At Leipzig, Latour-Maubourg was seriously wounded and replaced by Jean-Pierre Doumerc who led the corps for the remainder of the War of the Sixth Coalition which ended with Napoleon's abdication in 1814. After Napoleon returned from exile and retook power in France in 1815, the main French army was baptised Armée du Nord. The army included a I Cavalry Corps led by Pierre Claude Pajol which fought at Ligny and Wavre, while one detached division fought at Waterloo.
Document 5: Erich Ludendorff: Erich Friedrich Wilhelm Ludendorff (9 April 1865 – 20 December 1937) was a German general, the victor of the Battle of Liège and the Battle of Tannenberg. From August 1916, his appointment as Quartermaster general ("Erster Generalquartiermeister") made him the leader (along with Paul von Hindenburg) of the German war efforts during World War I until his resignation in October 1918, just before the end of hostilities.
Document 6: II Corps (Union Army): There were five corps in the Union Army designated as II Corps (Second Army Corps) during the American Civil War. These formations were the Army of the Cumberland II Corps commanded by Thomas L. Crittenden from October 24, 1862, to November 5, 1862, later renumbered XX Corps; the Army of the Mississippi II corps led by William T. Sherman from January 4, 1863, to January 12, 1863, renumbered XV Corps; Army of the Ohio II Corps commanded by Thomas L. Crittenden from September 29, 1862, to October 24, 1862, transferred to Army of the Cumberland; Army of Virginia II Corps led by Nathaniel P. Banks from June 26, 1862, to September 4, 1862, and Alpheus S. Williams from September 4, 1862, to September 12, 1862, renumbered XII Corps; and the Army of the Potomac II Corps from March 13, 1862, to June 28, 1865. Of these five, the one most widely known was the Army of the Potomac formation, the subject of this article.
Document 7: 2nd Royal Bavarian Division: 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."). 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.
Document 8: II Corps (United States): The II Corps was a corps-sized formation of the United States Army that was active in both World War I and World War II. It was originally formed and fought on the Western Front during World War I and was also the first American formation of any size to see combat in North Africa or Europe during World War II.
Document 9: Erich von Falkenhayn: General Erich Georg Anton von Falkenhayn (11 September 1861 – 8 April 1922) was the Chief of the German General Staff during the First World War from September 1914 until 29 August 1916. He was removed in the late summer of 1916 after the failure at the battle of Verdun, the opening of the Allied offensive on the Somme, the Brusilov Offensive and the entry of Romania into the war. He was later given important field commands in Romania and Syria. His reputation as a war leader was attacked in Germany during and after the war, especially by the faction which supported Hindenburg. Falkenhayn held that Germany could not win the war by a decisive battle but would have to reach a compromise peace; his enemies said he lacked the resolve necessary to win a decisive victory. Falkenhayn's relations with the Chancellor Bethmann-Hollweg were troubled and undercut Falkenhayn's plans.
Document 10: 2nd Army Corps (Russian Empire): 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.
Document 11: Schlieffen Plan: The Schlieffen Plan (German: "Schlieffen-Plan" , ] ) was the name given after World War I to the thinking behind the German invasion of France and Belgium on 4 August 1914. Field Marshal Alfred von Schlieffen, the Chief of the Imperial Army German General Staff from 1891 to 1906, devised a deployment plan for a war-winning offensive, in a one-front war against the French Third Republic from 1905–06. After the war, the German official historians of the "Reichsarchiv" and other writers, described the plan as a blueprint for victory. German historians claimed that the plan had been ruined by "Generaloberst" (Colonel-General) Helmuth von Moltke the Younger, the Commander-in-Chief of the German army after Schlieffen retired in 1906, who was dismissed after the First Battle of the Marne (5–12 September 1914).
Document 12: 2nd Army (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.
Document 13: Polish Armed Forces in the East (1914–20): Polish Armed Forces in the East around World War I is a term used for several Polish military formations formed in Russia and operating in the period of 1914–1920 (First World War, Russian Revolution of 1917, and the early stages of the Polish-Ukrainian War and Polish-Soviet War. Early formations were part of the Imperial Russian Army. Later, during the Russian Revolution, the Polish formations were mainly allied to the White Russian forces and the Western powers (both the German Empire and the Entente). All the formations (or their remains) were eventually incorporated into the Polish Army by 1920.
Document 14: 14th Mechanized Corps (Soviet Union): The corps was formed in March 1941 at Kobryn under the command of Major General Stepan Oborin as part of the 4th Army in the Western Special Military District. Colonel Ivan Tutarinov was its chief of staff. The corps' 22nd Tank Division was formed from the 29th Tank Brigade in the southern military camp on the outskirts of Brest. The 30th Tank Division was formed from the 32nd Tank Brigade in Pruzhany, later moving to Slobodka. The howitzer artillery regiments of the divisions were formed from howitzer artillery battalions of the 4th Army's rifle divisions. The 205th Motorized Division was formed and stationed in Bereza Kartuska and the surrounding villages. It was formed from the 3rd Motorized Machine Gun Artillery Brigade in the 42nd Rifle Division's barracks, after the 42nd had moved to Brest. The 205th Division had a low level of combat readiness. From mid-June the corps began creating a field command post in the area of Tevli. The corps was equipped with 534 tanks, most of which were the obsolete T-26. The corps had half of its authorized 1,031 tanks.
Document 15: 1st Army Corps (Russian Empire): 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.
ground_truth: World War I