By September 1914 the Russians had defeated the Austro-Hungarian offensive in Galicia at the Battle of Galicia leaving the Austrian fortress of Przemyśl besieged by the Russian Eighth Army. Nikolai Ruzsky had defeated the German’s first attempt at capturing Warsaw at the Battle of the Vistula River.
The Russian high command was split over how to capitalize on these recent successes. Grand Duke Nicholas Nikolayevich favored an offensive into East Prussia, while the Chief of Staff, Mikhail Alekseev, favored an offensive into Silesia.
Paul von Hindenburg had recently been appointed commander of the Central Powers along the Eastern Front. Hindenburg had intercepted Russian reports of the proposed invasion into Silesia, and saw an opportunity to repeat his crushing victory at the Battle of Tannenberg, by hitting the Russian flank as it moved into Silesia.
Hindenburg moved the German Ninth Army, under General August von Mackensen, to the Polish sector. Conrad von Hotzendorf, the Austrian commander, moved the Austrian Second Army to replace the German Ninth Army’s former position.
General Nikolai Ruzski had recently assumed command of the Russian Army Group defending Warsaw. Ruzski had under his command General Paul von Rennenkampf‘s Russian First Army which was positioned north of the Vistula River, with the exception of one corps that was on the south bank of the river. Ruzski also had the Russian Second Army under General Scheidemann, which was positioned directly in front of Łódź. The Russian Fifth Army, under Pavel Plehve, was ordered to abandon its Silesia offensive, and moved to help counter Hindenburg’s new offensive.
On November 11, Mackensen’s German Ninth Army struck the V Siberia Corps of Rennenkampf’s First Army which was isolated south of the Vistula and routed it, capturing 12,000 prisoners. The rout left a gap between the Russian First and Second Armies and the two forces lost contact with one another.
In the meantime Scheidemann’s Russian Second Army was being flanked and began retreating towards Łódź. The Russians were beginning to realize the seriousness of the situation in Poland. The Second Army was now being threatened with encirclement.
The Grand Duke was primarily concerned with saving this army and avoiding a repeat of Tannenberg. Wenzel von Plehve and the Russian Fifth Army had been ordered from Silesia to the Łódź sector and covered 70 miles in only two days. Von Plehve smashed into Mackensen’s right flank on November 18 under appalling winter conditions (at times the temperature dropped as low as 10 °F (−12 °C)).
At the same time from the east, along the banks of the Vistula, Germans were attacked by the columns of Rennenkampf’s Army. The Germans were now threatened with encirclement, but fought their way out by November 26, taking with them the prisoners from the Russian First Army. Pressure on Łódź continued until December but the Germans were unable to break the Russian lines. Short on ammunition, the Russians withdrew to form a new and stronger line closer to Warsaw.
The results of the Battle of Łódź were inconclusive, both sides having achieved their most important objectives. The Russians had repulsed the Germans and saved Warsaw, which had been the objective of the original German offensive. The Germans, for their part, had caused the Russians to abandon their offensive into Silesia.
The Russian high command had had enough of Rennenkampf and relieved him of his command, replacing him with General Litvinov.
Casualties and losses. Russian Empire: 110 000 killed, wounded or captured, German Empire: 160 000 killed, wounded or captured
My school semester will be wrapping up soon, and then I will resume composing my own posts. The above is taking from Wikipedia, which provides a very useful, thorough examination.