Nikonov’s threat might sound startling, but it’s in keeping with the current state of Russia’s ever-evolving policy on the use of nuclear weapons. While the Soviet Union maintained a policy against the first use of nukes, Putin’s government turned away from that strict prohibition in 2000 with the signing of a new military doctrine that allows for the limited use of nuclear weapons “in response to large-scale aggression utilizing conventional weapons in situations critical to the national security of the Russian Federation.”

Putin has also shown a growing willingness to invest in nuclear-weapons technology. In March, he vowed to put more money into new intercontinental ballistic missiles, so-called “strategic” nuclear forces, and to prioritize those military investments “above all” other areas.

But the type of nuclear weapons that Russia would use to defend its stolen territory in Crimea might be far smaller: sub-kiloton tactical devices dwarfed even by the roughly 15 kiloton Little Boy bomb dropped on Hiroshima in 1945. These small warheads have emerged as a big concern for U.S. military leaders.

The Russians “maintain their tactical nuclear stockpile in ways that we have not,” Maj. Gen. William Hix, the Army’s director of strategy, plans, and policy said in March at the Booz Allen Hamilton Directed Energy Summit.

Still, a growing nuclear arsenal doesn’t mean that Putin is itching to stage a sneak attack.

“There is little indication that Russia plans to use nuclear weapons at the outset of a conflict, before it has engaged with conventional weapons, even though Russia could resort to the use of nuclear weapons first, during an ongoing conventional conflict,” Amy Wolf, a nuclear weapons specialist with the Congressional Research Service, wrote in February . “This is not new, and has been a part of Russian military doctrine for years.”

NATO on the March

Why is the Russian government telegraphing its willingness to go nuclear in Ukraine? In a word, NATO. The Cold War-born treaty organization of Western nations may seem obsolete to some , but not to Russia, which has watched with concern as NATO has added a dozen eastern members that used to be under Moscow’s sway.

“For us, [NATO] is a military alliance spanning three-quarters of the global defense money, now planning to expand that figure,” said Nikonov.

In the two years since Russia annexed Crimea, NATO’s Baltic members have doubled their defense budgets. In 2018, Latvia, Lithuania, and Estonia are projected to spend nearly $670 million, up from $210 million in 2014. “This growth is faster than any other region globally,” Craig Caffrey, principal analyst at IHS Jane’s, remarked last October. “In 2005, the region’s total defense budget was $930 million. By 2020, the region’s defense budget will be $2.1 billion.”

NATO has been expanding its troop presence in Eastern Europe as well. In April 2016, during the Warsaw summit, NATO agreed to increase the size of the NATO force deployed to the Baltics, a posture move sometimes called enhanced forward presence . In January, the U.S. deployed some 4,000 troops to Poland. The following month, Germany announced that it would send some 1,000 troops to Lithuania.

It’s another mark of escalating tensions in the region due to continuing conflict in Ukraine and aggressive Russian activities across Europe, including a Kremlin-backed coup attempt in Montenegro in October, complete with an assassination attempt on former Prime Minister Milo Djukanovic. (Montenegro joined NATO in May.) Nikonov said these regional tensions, and their causes, are perceived very differently in Russia than in the West.

“For Russia, the definition of success in dealing with neighbors is to make them as friendly to Russia as possible,” he said at the GLOBSEC forum. “The definition of success for many people sitting in this room is how to distance those countries from Russia. I think these are conflicting goals.”