According to Prit Buttar: The Dual Alliance and Franco-Russian Treaty, and the obligations contained within them, would prove to be major mechanisms in the outbreak of war in 1914.

Germany defended East Prussia with the Eighth Army, commanded by Maximilian von Prittwitz, consisting of 100 battalions, supported by reserve and Landwehr formations.

[10]: 43, 64, 115 Anticipating that the Russians would attack north of the Rominter Heath, then west along the Pregel Valley, Prittwitz ordered Hermann von François' First Corps to take up positions along the Angerapp river.

[10]: 115–117 [11] On 15 August, François' men encountered First Army's reconnaissance units northeast of Stallupönen, and captured Eydtkuhnen that night as the Russians withdrew.

François called up General Adalbert von Falk's 2nd Division in Tollmingkehmen, and his howitzers in Gumbinnen, to reinforce his position in Stallupönen as the battle intensified by mid-day.

[8] But the actions of the 29th division had a decisive result, its counterattack to the rear of Francois created a threat of encirclement and the Germans were forced to stop the battle.