The war in the east was more complex and dynamic than the bloody war of attrition in the west. The “eastern” front also included what might be called the Balkan front, as well as the Italian Front, where the Austrian Empire was contested by the Italian army, which had switched sides in the conflict. In addition, the “east” contained the Asian front, where the British and its imperial allies fought with the Ottoman Empire over the Middle East and the Levant (the Near East or today's Lebanon, Syria, Israel/Palestine and Jordan).
In the East, the momentum of the war pulled in many directions. Germany, for example, scored massive victories in 1915 in the battle with Imperial Russia, pushing the Russians out of Poland and deep into the Ukraine and Belarus. Despite these impressive victories, the Germans were not able to deliver a decisive blow to the tsar’s army until after the revolutionary year of 1917. It would be Lenin and the Bolsheviks, not the tsar or the provisional government, that would make peace with the Germans at Brest-Litovsk, surrendering huge portions of territory to Germany in what many described as a "punitive peace."
To the south, the situation for the Central Powers was more ominous. The Austrians struggled against the Russians and failed to knock the Italians out of the war. By 1917-1918, the Italians had gained the upper hand, striking a decisive blow against the Austrian Empire in the Battle of the Piave River in June, 1918. Even more distressing for the cause of the Central Powers was the status of the Ottoman Empire, which was steadily shrinking into Anatolia as Britain and its allies secured the Middle East and the Levant, taking strategic and symbolically important sites like Baghdad, Jerusalem, and Damascus. By the time the Germans were able to push Russia out of the war, the situation to their southeast had deteriorated to such an extent that the victory was unable to shift the overall trajectory of the war. The threat of Austrian and Ottoman collapse continued to pose tremendous risk to the German war effort.
The central threat to the war effort of Germany and its allies, however, was not a military one on the eastern/southern front as much as it was one of provisions and supply. Lacking a global reach and failing to contest allied hegemony in the seas, the Central Powers had to rely on the principle of autarky—or self-sufficiency. As territory decreased and access to raw materials and foodstuffs vanished, pressures mounted on the military/industrial capacities, soldiers on the front, and populations at home. Throughout the Ottoman, Austrian, and German empires material deprivation was widespread. Populations starved. All available work and resources were poured into the war machine, and it was still not nearly enough. Modern war was the domain of modern states. States strong and flexible enough to adapt to the conditions of this warfare survived. Those too weak to withstand the pressures crumbled and disappeared: first Russia, then Austria, and then the Ottoman Empire.