Eighteen soldiers died over the weekend as the deadliest clashes in two decades broke out between Armenia and Azerbaijan, over the mountainous region of Nagorno-Karabakh.

The roots of the conflict go back to Joseph Stalin’s rule of the Soviet Union. Stalin deliberately drew the borders of soviet states so that each republic would struggle to be a prosperous viable state if they ever gained independence. So he made Nagorno-Karabakh, where most were Armenian, part of Azerbaijan.

Then in late ’80s, as the Soviet Union crumbled and as both nations became more independent, Stalin’s borders caused war. Hundreds of thousands fled the region. By the time the war ended in 1994, around 30,000 had been killed.

Since then, the dispute has remained a so-called “frozen conflict.” The 1994 ceasefire left Armenia in possession of Nagorno-Karabakh, but neither Azerbaijan nor the international community recognize this.

Armenia is backed by Russia, with Azerbaijan supported by Turkey—though Azerbaijan is always careful not to stray too far from Russia. Armenia has said it will join Russia’s Eurasian Union, while Azerbaijan is closer to the EU.

It is not clear how the recent fighting began, who the aggressor was, or even if the whole thing blew up because of some kind of accident. Azerbaijan reports that 13 of its soldiers died, while the Armenian Nagorno-Karabakh forces reported five causalities. Since the initial fighting over the weekend, both sides have continued to fire on each other.

Both presidents will travel to Sochi on August 8 to meet with Russian President Vladimir Putin.

In terms of how this will play out, all we have so far is speculation. If the flare up is the result of an accident, it will probably die down.

Azerbaijan knows that picking a fight with Armenia is picking a fight with Russia. But Azerbaijani President Ilham Aliyev has been talking tough. “Today, the Azerbaijani Army is capable of destroying any object in Nagorno-Karabakh,” he said on August 6 as he traveled to Azerbaijan’s border with the region. “This is known to us and the people of Azerbaijan. Let this also be known to the enemy.”

Perhaps Azerbaijan has decided that Russia is too preoccupied with Ukraine to come to Armenia’s defense. It could be backed by outsider powers, looking for an opportunity to punish Russia. Or on the other hand, if Armenia started the conflict, perhaps Russia is warning Azerbaijan that it’s drifted too close to the West for Russia’s liking.

Whatever is going on, this is another area of conflict where we could soon see Russia assert its power, which could pit Europe against Russia even more.