Title: Eastern Front (World War I)
Content:  With the end of major combat on the Eastern Front, the Germans were able to transfer substantial forces to the west in order to mount an offensive in France in the spring of 1918. This offensive on the Western Front failed to achieve a decisive breakthrough, and the arrival of more and more American units in Europe was sufficient to offset the German advantage. Even after the Russian collapse, about a million German soldiers remained tied up in the east until the end of the war, attempting to run a short-lived addition to the German Empire in Europe. In the end, the Central Powers had to relinquish all of their captured lands on the eastern front, with Germany even being forced to cede territory they held before the war, under various treaties (such as the Treaty of Versailles) signed after the armistice in 1918.
Title: German invasion of Belgium (1914)
Content:  and Seine, by short, rapid attacks, unable to withdraw into central France. The French would either be annihilated or the maneuver from the north would create conditions for victory in the centre or in Lorraine, on the common border. A corollary to the emphasis on the Western Front was a lack of troops for the Eastern Front against Russia. In the east the Germans planned a defensive strategy and relied on the Austro-Hungarian Army (Landstreitkräfte Österreich-Ungarns/Császári és Királyi Hadsereg) to divert the Russians from East Prussia, while France was crushed. Divisions from the German army in the west (Westheer) would be redeployed to the East to deal with the Russians as soon as a breathing-space was gained against the French.
Title: Paul von Hindenburg
Content:  In the spring of 1916, the Central Powers experienced a military catastrophe in the East that left Germany bearing much of the war effort until the end of hostilities. On 4 June, the Russian Army began a massive offensive along 480 km of the southwestern front in present-day western Ukraine. In the ensuing onslaught, four armies commanded by General Aleksei Brusilov overwhelmed entrenchments that the Austro-Hungarians long regarded as impregnable. Probing assault troops located three weak spots which then were struck in force. In nine days they captured more than 200,000 men and 200 guns, and pushed into open country. Austro-Hungarian troops were rushed back from the Italian Front. Every man was needed in the west, so German troops on the Eastern Front had to be 
Title: History of Germany during World War I
Content:  were very successful, particularly in the Battle of the Frontiers (14–24 August). By 12 September, the French with assistance from the British forces halted the German advance east of Paris at the First Battle of the Marne (5–12 September). The last days of this battle signified the end of mobile warfare in the west. The French offensive into Germany launched on 7 August with the Battle of Mulhouse had limited success. In the east, only one Field Army defended East Prussia and when Russia attacked in this region it diverted German forces intended for the Western Front. Germany defeated Russia 
Title: World War I
Content:  the East were larger. The Germans did well at the First Masurian Lakes driving the invaders from East Prussia, and at Riga, which led the Russians to sue for peace. The Austro-Hungarians and Germans joined for a great success at Gorlice–Tarnów, which drove the Russians out of Poland. In a series of attacks along with the Bulgarians, they occupied Serbia, Albania, Montenegro and most of Romania. The Allies successes came later in Palestine, the beginning of the end for the Ottomans, in Macedonia, which drove the Bulgarians out of the war, and at Vittorio Veneto, the final blow for the Austro-Hungarians. The area occupied in the East by the Central powers on 11 November 1918 was 1042600 km2.
Title: Romania in World War I
Content:  by the Central Powers on 3 September 1917 marked a strategic defeat and a considerable weakening of their forces on the South-Eastern front. The response of the Romanian army in fact created the strongest blow to the Central Powers that was dealt in Eastern Europe in 1917. As a result of these operations, the remaining Romanian territories remained unoccupied. Nearly 1,000,000 Central Powers troops were tied down, and The Times was prompted to describe the Romanian front as "The only point of light in the East". On 22 September, Romania achieved its greatest naval success of the war, when the 
Title: Curious Notions
Content:  The Central Powers win by managing to knock out France and the British Expeditionary Force in the west towards the beginning of the war. Then they defeat Russia before the United States can intervene. A few years later, the German Empire intervenes in the Russian Revolution and defeats the Bolsheviks, but the Russian Empire is mostly divided and therefore no longer a great power. Britain and France tried to stop Germany's power again in the late 1930s, but since the United States does not intervene, they lose and Germany gains control over Europe and its sphere of influence. Germany is also able to restore the monarchies of Brazil, China and 
Title: Central Powers
Content:  Guinea and German East Africa, until almost all of their colonies were occupied by the Allies. The Central Powers faced and were defeated by the Allied Powers that had formed around the Triple Entente. The Central Powers' origin was the alliance of Germany and Austria-Hungary in 1879. Despite having nominally joined the Triple Alliance before, Italy did not take part in World War I on the side of the Central Powers. The Ottoman Empire and Bulgaria did not join until after World War I had begun, even though the Ottoman Empire had retained close relations with both Germany and Austria-Hungary since the beginning of the 20th century.
Title: Eastern Front (World War I)
Content:   In 1915 the German command decided to make its main effort on the Eastern Front, and accordingly transferred considerable forces there. The year began with a successful German offensive in the area of the Masurian lakes. At the same time, a large battle for the city of Prasnysch took place on the Polish front. The city changed hands several times but eventually remained in Russian hands. As a result of the battle, the Germans lost 38 000 soldiers, Russian losses amounted to about 70 000 men. In May 1915, to eliminate the Russian threat the Central Powers began the successful Gorlice–Tarnów Offensive in Galicia. After the Second Battle of the Masurian Lakes, the German and Austro-Hungarian troops in the Eastern Front functioned under a unified command. The offensive soon turned into a general 
Title: Late modern period
Content:  1917, defeated the Central Powers, led by the German Empire, Austro-Hungarian Empire and the Ottoman Empire. The war caused the disintegration of four empires—the Austro-Hungarian, German, Ottoman, and Russian ones—as well as radical change in the European and West Asian maps. The Allied powers before 1917 are referred to as the Triple Entente, and the Central Powers are referred to as the Triple Alliance. Much of the fighting in World War I took place along the Western Front, within a system of opposing manned trenches and fortifications (separated by a "No man's land") running from the North Sea to the 

Question: who did the central powers defeat on the eastern front before concentrating back on france?
Answer: the Russian army.