Beginning Thursday, as many as 100,000 Russian and Belarusian troops will launch major military exercises along the border of three NATO countries.

Russia’s upcoming Zapad military exercise, which will simulate a response to an attempted overthrow of the Belarusian government by an insurgency unfriendly to Russia, has European countries and the United States on edge at a time when relations between the NATO alliance and Moscow are colder than ever.

Zapad has the potential to be the country’s largest military exercise since the Cold War – despite Russian claims that only roughly 13,000 troops will participate, Western defense officials have put forward estimates closer to 100,000. Many suspect the Russians may hold multiple, smaller, simultaneous exercises as unofficial parts of Zapad, to adhere to the letter, if not the spirit, of the official 13,000 limit.

Why 13,000? According to the Vienna document, an agreement among the nations of the Organization for Security and Co-operation in Europe of which Russia is a member, any exercise involving more than 13,000 people – including both military and support personnel – requires that outside observers be allowed to attend. NATO Secretary General Jens Stoltenberg said last week that Moscow’s offer to allow three international observers access is not sufficient.

What is of more concern than the actual numbers are NATO fears of Russian duplicity. Russia made similar assurances regarding troop numbers in 2013, ahead of the last Zapad exercise, but the number reached nearly 70,000 – and acted as a prelude to the 2014 annexation of Crimea from Ukraine.

So, is this Russian posturing or a true threat to NATO? According to experts, the exercises pose three major risks: potential positioning for a future attack, as in 2014; diversion for Russian activities elsewhere, such as in Syria and Ukraine; and an opportunity to signal to its Western rivals that it is once more a player on the global stage. None of these options are mutually exclusive, and all also carry the potential for miscommunication or miscalculation that leads to actual conflict.

The exercise comes at a time when the U.S. and Russia are exchanging diplomatic blows by expelling each other’s diplomats (because of the U.S. assertion that Russia interfered in the 2016 presidential election) and subtly challenging each other across the world from Syria to Afghanistan.

Former U.S. Senior Defense Official and Military Attaché to the Russian Federation, retired Brigadier General Peter Zwack, told The Cipher Brief, “I haven’t seen this level of distrust in my experience since 1999 – Kosovo. It is built on the 2014 crisis points and exacerbated by the very ugly activities – corruption and meddling – in our own body politic.” Given that level of tension, Zwack’s main concern surrounding Zapad is “an accident or an incident in this period of really serious distrust.”

Meanwhile, Russia’s primary objective seems clear: sending an indisputable message of strength to its Western neighbors and their NATO allies. In fact, the name Zapad, which means “West” in Russian, is quite literal – Belarus shares a western border with three NATO countries: Poland, Lithuania, and Latvia.

Speaking to the BBC on Sunday, UK Defense Secretary Michael Fallon indicated that the message was not lost on Europe: “This is designed to provoke us, it’s designed to test our defenses, and that’s why we have to be strong,” he said. “Russia is testing us and testing us now at every opportunity.”

Indeed, the Russian First Guards Tank Army – the historic unit that fought back the German invaders in World War II along the Eastern Front and then went on to occupy Berlin during the Cold War – will participate in the exercise.

The message was certainly not lost on Russia’s eastern European neighbors either. General Jaroslaw Stróżyk, the former Polish Defense Attaché in the United States, told The Cipher Brief that “the major aim of Zapad-17 is to intimidate Poland, Estonia, Latvia, and Lithuania.”

Beyond messaging, the West will also be watching closely for signs that Russia may be leaving military equipment in Belarus as pre-positioning for a future attack on one of the bordering nations – making Zapad-17 a modern-day Trojan Horse.

The Commander of U.S. Special Operations Command, General Tony Thomas, stated in July that “the great concern is that [the Russians] are not going to leave” Belarus after the conclusion of the exercise. “And that’s not paranoia,” he added.

Moreover, after the 2014 Russian annexation of Crimea and its intervention in Syria, experts noted similarities between tactics used in those actions, such as the use of unmanned aerial systems, and maneuvers practiced in Zapad-13.

But that also creates an opportunity for NATO, according to Cipher Brief expert and former member of the CIA’s Senior Intelligence Service Steven Hall.  “There’s going to be the entire breadth of NATO collection capabilities aimed at Zapad to try to find out what the Russians are capable of,” he told The Cipher Brief.

So what does NATO have planned during the exercise?

According to NATO officials, the alliance will “closely monitor exercise Zapad-17 but we are not planning any large exercises during Zapad-17. Our exercises are planned long in advance and are not related to the Russian exercise.”

Instead, NATO will maintain normal military rotations, while carrying out previously scheduled exercises in Sweden, Poland, and Ukraine. Sweden, which is not a NATO member but is a member of the European Union, began its Aurora 17 exercise on Monday – which consists of 20,000 people from nine Western countries, including around 1,000 U.S. Marines, training to counter a hypothetical attack by Russia.

There will also be an additional six-week deployment of three companies of 120 paratroopers to each of the three Baltic countries for ‘low-level’ exercises. And, based on a 2016 agreement, four deployments of U.S., UK, German, and Canadian troops maintain an “Enhanced Forward Presence” in Latvia, Lithuania, Poland, and Estonia.

However, according to Zwack, NATO’s readiness needs to go beyond the military component. The alliance must be “absolutely ready” from a political and economic perspective as well, and prepared to lay down “mind-bending sanctions” if the Russians move beyond exercises to “a permanent dwell” in Belarus.

Russian adventurism, he believes, must have consequences that would put the Russian regime – and the monied interests that support that regime – at risk. It would need to be, according to Zwack, an existential threat to the controlling powers in Russia: in other words, “bad for business.”

But even if the exercise concludes without incident, the current climate is simply unsustainable, according to General Philip Breedlove, the former U.S. Supreme Allied Commander in Europe, who retired in 2016.

“I would hope that cooler heads and better judgment would prevail. But we can’t live in this way,” he told The Cipher Brief, adding, “The glib saying you often hear is ‘hope is not a strategy.’”

Originally Published: The Cipher Brief on Wednesday, September 13, 2017 – 22:30