As night fell on Monday, the death toll since hostilities erupted on Friday stood at 46. The following day, both Azerbaijan and Armenian separatist forces declared an immediate ceasefire.
Tensions date back to the collapse of the Soviet Union. In 1988, Nagorno-Karabakh, a majority Armenian oblast within Soviet Azerbaijan, sought to unite with nearby Armenia. A full-scale war began in 1992 between the former Soviet republics of Armenia and Azerbaijan over control of the mountainous, disputed territory.
Some 30,000 people died and nearly a million people were displaced by the violence before a Russian-brokered cease-fire brought a modicum of calm in 1994. Around 700,000 ethnic Azeris were forced out of Nagorno-Karabakh and surrounding areas, where a separatist government declared de facto independence, though the region is still considered part of Azerbaijan by the international community. The status of a vast majority of these refugees is still unresolved, more than two decades later.
The conflict also saw 235,000 Armenian refugees flee other parts of Azerbaijan, including from Nakhichevan, an exclave of Azerbaijan tucked between Armenia and Turkey.
A slow-moving peace process was launched thereafter under the aegis of the Organization for Security and Cooperation in Europe, an international institution aimed at bringing stability to the restive post-Soviet world. It has so far been unable to forge a lasting agreement around Nagorno-Karabakh; the boundary between areas controlled by Azerbaijan and ethnic Armenian forces is now perhaps Europe's most militarized fault-line.
A regional tinderbox
Armenia's semi-democratic government helps prop up the separatists in Nagorno-Karabakh; it's unclear whether some of the Armenian soldiers slain in the recent clashes were separatist militia or actual troops from Armenia.
Because of an oil boom over the past decade, Azerbaijan's authoritarian leadership was able to increase its military expenditure twenty-fold between 2004 and 2014. Two years ago, entrenched President Ilham Aliyev boasted that his country's military budget alone was greater than all of Armenia's budgetary spending.
Both sides accuse the other of provoking this weekend's violence and have little incentive to back down from their adversarial positions.
"Armenia’s leadership lives and dies by its ability to hold on to the territory, and so has a clear interest in maintaining the status quo," writes Kevork Oskanian, a researcher at the University of Birmingham. "Azerbaijan’s government on the other hand, under pressure to 'liberate' the region, has become disillusioned with the deadlocked negotiations, and the recent fall in oil prices has hit Azerbaijan’s economy hard."
"Either there was an accidental breakdown of the ceasefire, started by either side, that was allowed to escalate before both sides suffered heavy losses and decided to stop," de Waal wrote. "Or, Azerbaijan decided to try to launch a small military operation to try to 'change the facts on the ground' that would tilt the situation more in its favor and recapture lost lands -- and Azerbaijan is indeed saying it captured some small pieces of territory."
Whatever the case, there's now a palpable sense of crisis, which has not dimmed despite the entreaties of the international community, including the United States.
"A further escalation of military action could lead to unpredictable and irreversible consequences, right up to a full-scale war," said Armenian President Serzh Sarksyan at a meeting with foreign ambassadors in the capital Yerevan on Monday.
The shadow of geopolitics
The rivalry between Armenia and Azerbaijan invariably has wider echoes. Armenia, a majority Christian nation, has in recent years grown closer to Russia, while Azerbaijan, whose population is majority Turkic Muslim, has received strong backing from neighboring Turkey.
Turkish President Recep Tayyip Erdogan condemned Armenia and its proxies for the violence.
"The fire of Armenia's massacres in Karabakh continues to burn in our hearts," Erdogan said on Monday, referring to the death of 12 Azerbaijani soldiers. "Karabakh will surely be returned to its rightful owner, Azerbaijan, one day."
Relations between Turkey and Armenia are understandably frosty as it is, in part because of Turkey's continued reluctance to recognize the hideous massacres and deportations of ethnic Armenians that took place a century ago as genocide. They are further complicated by Russia's own ties to Armenia, which is a Russian military ally and a member of a Moscow-led economic bloc.
Moscow and Ankara have been in crisis since Russia's intervention in the Syrian conflict last year, a move that had a disastrous impact on Turkish policy. It's not surprising that Turkish-Russian animosity would shadow another conflict in their respective back yards -- one which happens to be taking place over a vital transit route of oil and gas to Europe.
But Russia has played something of a double-game in the region, selling armaments to both Armenia and Azerbaijan while also trying to push through various unsuccessful peace deals.
"Moscow is more closely involved than the other outside actors, and seems to pursue its own strategic interests," writes Magdalena Grono of the International Crisis Group. "Key among them is a closer link with Azerbaijan and proving its own indispensability on the regional stage as a mediator and security guarantor. Moscow will likely use its leverage to enhance its own standing in the region."
It may have to use that leverage soon in order to stave off a deadly spiral of violence.
More on WorldViews