Many had feared a day like this for years and now it has arrived. Reports from the ceasefire line of the Nagorny Karabakh conflict speak of fighting and dozens of soldiers being killed.

The Armenian-Azerbaijani conflict over Karabakh is not “frozen” as it is often misleadingly termed. The 1994 truce there has held due to the restraint and political calculation of the Armenian and Azerbaijani leaders, who have decided that it is not in their interests to go back to war with one another over the disputed territory.

But in recent years the situation has become a lot more dangerous. When the war ended in the 1990s, the Line of Contact dividing the two sides was a relatively quiet zone with barbed wire and lightly armed soldiers sitting in trenches.

In the last decade, Azerbaijan has used billions of dollars of its oil wealth to buy a formidable arsenal of new weapons, including helicopters, drones, MiG aircraft, and heavy artillery, many of them purchased from Russia. Armenia has also strengthened its defenses, also mainly with weapons acquired from Russia (but at discounted prices).

With all these heavy weapons, around 20,000 men on either side, and just six unarmed OSCE monitors in the conflict zone, the potential for a serious outbreak of fighting has never been greater.

Everyone knows that a new Karabakh war would not just be tragic for Armenia and Azerbaijan, but devastating for the entire South Caucasus region.

The first indications are that this is indeed the worst violence since the ceasefire of May 1994. In the last 24 hours, both sides have reported heavy casualties, including among civilians. The Azerbaijani side says it has captured strategic heights in the northeast of Karabakh, destroyed six tanks, and killed more than 100 on the Armenian side.

The Karabakh Armenian authorities claim to have killed more than 200 Azerbaijani soldiers.

Armenian side reports that it has destroyed one Azerbaijani helicopter, two drones, and three tanks. The Armenian Defense Ministry released a video that showed a downed drone and ruined houses.

This is more than the customary resumption of low-level violence that is often observed in the spring, when the snows melt in the highlands of Karabakh and soldiers begin shooting at one another.

This is something much more serious. Big violations of the Karabakh ceasefire tend not to be accidents but to have a political cause. There are strong vertical chains of command from the officers on the ground to the presidents in Baku and Yerevan.

The Azerbaijani side has more reason to break the ceasefire. As the losing side in the conflict of the 1990s, when it lost almost one seventh (or about 13.6 percent) of its de jure territory to the Armenians, Baku knows that one of its few tools of pressure on the Armenians is to violate the ceasefire and remind them that the status quo can be shaken.

However, once fighting begins, it becomes irrelevant who started it, as the Armenian side is capable of conducting military operations of its own into Azerbaijani-controlled territory on the other side of the line. Pictures from Azerbaijan show civilians leaving the conflict zone, some of them on foot.

The Azerbaijani media have been citing the four UN resolutions of the 1990s, which call for Armenian military withdrawal from the conflict zone, as if to remind the world of Azerbaijan’s right to use military force.

The most curious aspect of this is that both presidents, Ilham Aliyev and Serzh Sargsyan, have been in Washington attending President Obama’s Nuclear Summit. Both men had serious discussions with senior U.S. officials such as Secretary of State John Kerry and Vice President Joe Biden. However, the U.S. government was unable to arrange for a bilateral meeting between the Armenian and Azerbaijani leaders.

This naturally leads to speculation about why the fighting should start at this particular moment.

Any analysis of this is pure guesswork. One line of thinking is that Moscow may have somehow managed to provoke the fighting in order to discredit the reputation of the United States as a peacemaker—even though Russia and the United States are still formally partners as two of the three co-chairs of the OSCE Minsk Group.

Under this scenario, President Vladimir Putin can then intervene as the real peacemaker between the two sides and demand a peace deal that includes Russian peacekeepers on the ground.

The trouble with this theory is that Russia, although the most important secondary actor in the Karabakh conflict, does not control the situation on the ground. It is not powerful enough to make the Armenian or Azerbaijani military forces do as it wants. They are strongly independent bodies, answerable only to their own presidents. Russia’s ability to shape events is probably smaller than it looks.

It is more likely that one of the two parties to the conflict—and more likely the Azerbaijani side, which has a stronger interest in the resumption of hostilities—is trying to alter the situation in its favor with a limited military campaign.

The dangerous aspect to this is that, once begun, any military operations in this conflict zone can easily escalate and get out of control. An unpredictable conflict environment combines with a tough macho political culture where it is seen as a sign of weakness to compromise. And, as the Prussian general Helmuth von Moltke said, “No battle plan ever survives contact with the enemy.”