War with Armenia
Leaving Baku we would need to head north into Georgia because the border with Armenia is a war zone. So it's not possible to cross it, at least not in a tour coach, with any safety. The present enmity dates back to 1917 but the roots are much earlier, perhaps going back to the 12th century and the arrival of Islam; or to the fourth century and the arrival of Christianity; or perhaps even to the 5th century BCE and the arrival of Zoroastrianism?
Coming forward to modern times, from the turn of the 19th century Tsar Nicholas II (the bloody) had made a series of catastrophic military mistakes that got worse at the start of the First World War. So Russia was in turmoil, culminating in the first revolution at the beginning of 1917. As a result the Russian Army of the Caucuses was withdrawn and the (Turkish) Ottoman Empire saw an opportunity to invade. Muslim Azerbaijanis for their part saw their chance for independence. But it did not go smoothly. A bloody civil war broke out between ethnic (Christian) Armenians, who remembered the Armenian Genocide in Turkey, and (Muslim) Azerbaijanis, supporting the Turks.
Then in October there was a second, Bolshevik, Revolution in Russia and the Russian Civil War began. In Transcaucasia, particularly in Georgia, the Bolsheviks had been opposed by the Mensheviks (see later) and now inroads were being made by the anti-revolutionary forces known as White Russians (remember Dr Zhivago), who enjoyed initial military success here with western support.
David Lean (movie) and Boris Pasternak (book) - a very popular story in the West during the Cold War
source: public domain
So neither side were in a position to stop the sectarian violence in Azerbaijan. In 1918 a new, but short lived, Azerbaijani Democratic Republic was declared by the separatists but failed to stop the fighting. Social stability was not restored until 1920 when the Russian Civil War ended in a Bolshevik victory. The Russians then prevailed and an Azerbaijani Soviet was established under Lenin. People who had taken part in that violence were still unsatisfied and old memories, passed on to new generations, die hard. So traditional enmities and disputes over territory flared up again when the Soviet Union collapsed and the Russians withdrew, yet again. Our local guide made his still bitter partisan feelings on these matters quite clear.