As much as the 1917 Russian Revolution affected the course of World War I on the Eastern Front, I think there’s a pretty strong argument to be made that its biggest effects were felt in another of the war’s innumerable theaters: the Caucasus. While Russian forces in Eastern Europe had largely struggled almost from the war’s outset, apart from the Pyrrhic 1916 Brusilov Offensive, they’d steadily driven the Ottoman front line out of the Caucasus and into central Anatolia by early 1916, when Mustafa Kamal was put in charge of the front and managed to stem the bleeding. But when Russia itself descended into political chaos in 1917, and then pulled out of the war altogether after the Bolshevik takeover in October/November, the Ottomans were able to go on an offensive that continued through the end of the war. Although the Ottomans came out of the war as losers, and in fact stopped being “the Ottomans,” so thorough was their loss, the position of modern Turkey’s eastern borders owes a lot to the Caucasus Front’s 1917 change in fortunes.
There’s no question that the Armenian people suffered more than any other group on the Caucasus Front. Not only were they living right on the Ottoman-Russian front line, but Ottoman losses 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. 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 even more damning, even though these were Russian (eastern) Armenians, not Ottoman (western) Armenians. 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 toxic blend of arrogance and incompetence. No, it must have been Armenian treachery. The result of this scapegoating was, for Armenians living under Ottoman rule, genocide, and for Armenians who had been living under Russian rule, the very real threat of military extermination. With the Russians out of the war, those Armenians lost their only real protection against an Ottoman army that was looking to take back the territory it had lost, and to extract punishment from the people its government was blaming for their past humiliations.
Obviously we know today that, as bad as things got for the Armenians, they were thankfully not exterminated. The Ottomans advanced deep into Armenian territory after the Russians withdrew, but their advance was eventually stopped, owing to Armenian successes in three small battles 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 grind the Ottomans down until they were unable to continue their offensive and had to pull back (though this was not accomplished without cost; the civilian population of Karakilisa was massacred by the Ottomans, around 4000 people). It’s probably fair to say that, had Armenian forces not managed to win these three battles (or at least a couple of them), there’s a good chance there wouldn’t 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), and 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 Ottomans were still in a position to dictate terms, but the resulting Treaty of Batum that was signed on June 4 ceded somewhat less Armenian territory to the Ottomans than had been previously discussed in the conference, and, importantly, was recognition of Armenia’s existence as an independent nation. Georgia also concluded a less punitive peace agreement with the Ottomans as part of the treaty, while Azerbaijan’s part of the deal actually took the form of an alliance with the empire.
There was more fighting on the Caucasus Front after Batum. Armenian irregulars resisted Ottoman rule in parts of Armenia that had been give to the Ottomans by the treaty, and this went on until the end of the war, when Ottoman forces were obligated to leave the region. Georgia signed the Treaty of Poti, a defense pact with Germany, on May 28, and subsequent Ottoman-Azerbaijani activity in the Caucasus nearly brought the Ottomans into full-on conflict with their German allies. 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 near Baku. This was one of the final engagements of World War I, but it was 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 tamped down when both were Soviet republics, is still with us today.