It goes without saying that the 1917 Russian Revolution had a considerable impact on the course of World War I. It eliminated the Russian threat on the eastern front, for example, which is the part everybody learns about in history class. But it’s biggest impact may actually have been on the Caucasian front. This is largely because, while Russian forces in Eastern Europe had struggled almost from the war’s outset, in the Caucasus they’d steadily driven the Ottomans back, pushing the front line all the way into central Anatolia by the middle of 1916. It was at that point when the Ottomans wisely decided to put their most successful battlefield commander, Mustafa Kamal, in command on that front, and he managed to stem the bleeding. But when Russia first descended into political chaos and then pulled out of the war altogether, the Ottomans were able to go on the offensive through the end of the war. Although the Ottoman Empire lost the war in the end–so thoroughly that it stopped being the Ottoman Empire, in fact– it was this late-war surge that established the eastern border of modern Turkey.
With Russia handling its own internal problems, it was the Armenian people who bore the brunt of the change in Ottoman fortunes. The Armenian genocide was already well underway by this point, having begun all the way back in 1914-1915 when Ottoman authorities began forcibly deporting and/or detaining large numbers of Armenians who were viewed as a potential fifth column in the war against Russia. Armenian nationalism had been on the rise since the mid-1800s, which made their loyalty to the empire suspect, and the fact that many Armenian volunteers fought in the Russian army on the Caucasian and Persian fronts was still more damning–even though these were eastern Armenians, who lived in the Russian Empire, and not the western Armenians who lived within the Ottoman Empire.
As events transpired in the early years of World War I, the conditions for Armenians in the empire only worsened. Ottoman defeats, and the political pressure they created, led imperial leaders like War Minister Enver Pasha to look for a scapegoat, and the Armenians were an easy choice. It was determined that the Ottomans were losing in the Caucasus not because their forces were less capable than the Russians, or because leaders like Enver Pasha exhibited a problematic blend of arrogance and incompetence. No, it must have been Armenian treachery. The effect was, for Armenians living under Ottoman rule, genocide. For Armenians who had been living under Russian rule, once Russia was out of the war they faced the very real threat of military annihilation by an Ottoman army that was looking to take back the territory it had lost and to extract punishment from the people its government had decided were the Real Menace.
The genocide within the Ottoman Empire continued through the founding of the Turkish Republic (historians generally place its end date in 1923). But Armenians outside the empire were spared military destruction in no small part because of three relatively minor Armenian victories in late May 1918: the Battle of Karakilisa (now called Vanadzor), which ended on May 28, and the Battles of Sardarabad (near modern Nor Armavir) and Abaran (Aparan), both of which ended on May 29. In all three cases the Armenians were outnumbered and outgunned, but were nonetheless able to hold the Ottomans off until they had to pull back (though this was not accomplished without cost–the civilian population of Karakilisa, around 4000 people, was massacred by the Ottomans). Had the Armenians not won these three battles (or at least a couple of them), there might not be an Armenia today.
There were two immediate results to this trio of Armenian victories. First, the Republic of Armenia declared its national independence (from the Transcaucasian Democratic Federative Republic, the political entity that had formed to fill the vacuum left by the Russian withdrawal) as of May 28 (though the declaration was issued on May 30 and made retroactive). Second, there was a renewed push to negotiate an end to hostilities. A conference had begun on May 11 in the Black Sea port city of Batumi (which is now in Georgia), attended by Ottoman, Armenian, Georgian, and Azerbaijani (Georgia and Azerbaijan had both declared their independence around the same time as Armenia) representatives. The June 4 Treaty of Batum won Ottoman recognition of Armenia’s independence and left it more territory than the Ottomans had been willing to concede before the three May battles.
There was more fighting on the Caucasus Front after Batum. Armenian irregulars resisted Ottoman rule in those parts of Armenia that the treaty had given to the empire. This went on until the end of the war, when the Ottoman surrender and subsequent Turkish War of Independence threw things into chaos. Britain, along with the Armenians and some White Russian forces, unsuccessfully fought the Ottomans and Azerbaijanis in the August-September Battle of Baku, for control of oilfields in modern Azerbaijan. This was one of the final engagements of World War I, but it was also one of the first engagements in the Armenian-Azerbaijani War of 1918-1920. That war created a rift between the two Caucasian nations that, though it was suppressed when both were Soviet republics, has continued to the present day.