In April of 2013, American tanks briefly left European soil entirely for the first time since the invasion of Normandy in 1944. By January of 2014, however, American M1A1 Abrams tanks had returned to their German bases.

The departure of American tanks from Europe, Stripes reported, coincided with a drawdown of American forces and the inactivation of two infantry brigades. “The Abrams tanks will join 33 M2A3 Bradley infantry fighting vehicles and dozens of other heavy support vehicles that will be positioned at Grafenwöhr to be used at the training facilities there, at the Joint Multinational Readiness Center at Hohenfels and at other training areas across Europe,” Stripes revealed.

The reintroduction of American armor proved fortuitous. Just weeks later, Russian armed forces invaded the Crimean Peninsula in Ukraine. Soon afterward, pro-Russian separatists began the process of destabilizing the eastern portions of that country. They were later joined by regular Russian armed forces.

With that conflict still raging nearly one year later, the United States Army revealed its intention to bolster defenses in NATO nations which were formerly solidly within the Soviet sphere: The Baltic states (Estonia, Latvia, and Lithuania) and Poland.

Lt. Gen. Frederick “Ben” Hodges told reporters with Military Times (via The Washington Times) that the U.S. was sending “100 Abrams tanks and Bradley Fighting Vehicles” to Eastern Europe in order to deter further Russian aggression.

“We are looking at courses of action for how we could pre-position equipment that we would definitely want to put inside a facility where it would be better maintained, that rotational units could then come and draw on it and use it to train, or for contingency purposes,” Hodges said in a briefing from Vilnius, Lithuania.

Hodges visited a training site in Lithuania that could be used to store armor and said he would look at similar sites in Estonia and Poland.

“Certainly, I don’t see a need to build infrastructure — a FOB [Forward Operating Base] if you will — or anything like that, that would be used for U.S. forces,” Hodges said.

Hodges expressed his concern that America’s troop presence in Europe today only numbers 31,000, well below its Cold War height of 280,000. He added, however, that he does not believe Russia has any intention of mounting a massive conventional attack on NATO-allied forces because it would trigger a collective military response.

“I think that what they [the Russians] do want to do is to create that ambiguity, plant the seeds of uncertainty so that the alliance members lose confidence that the rest of the alliance would come to their aid if they were, in fact, attacked,” Hodges added.

That is not an unfounded concern.

The University of London’s economics professor Michael Ben-Gad recently told The Telegraph that the NATO border states are increasingly concerned about NATO’s resolve to come to their aid if they did invoke Article 5 of that treaty. He added that, because NATO presently lacks the military capability in theater to repel a Russian conventional attack, the only alternative would be for the West to threaten to respond to Russian aggression with nuclear weapons. Ben-Gad observed that Western capitals would likely refuse to “risk nuclear war in order to defend the sovereignty of Estonia.”

This is no hypothetical as Time Magazine’s Simon Shuster explained in September:

Take, for instance, the standoff unfolding along the Russian border with Estonia, one of the NATO allies that is, by virtue of geography and demography, most susceptible to Russian meddling. Not only does it share a border with Russia that is nearly 200 miles long, but its population is roughly a quarter Russian, forming an ethnic minority whose rights Putin has promised to “protect” by any legal means. These vulnerabilities were among the reasons Barack Obama chose to visit Estonia on Wednesday in a show of solidarity. During a speech in the capital, the U.S. President pledged his military would come to Estonia’s defense if it were ever attacked or invaded. “An attack on one is an attack on all,” Obama said, echoing Article 5 of NATO’s founding treaty, which obliges all members to defend any ally that faces a foreign attack.

Two days later, as the summit in Wales was winding down, Estonian President Toomas Hendrik Ilves sounded the alarm over what he reportedly called an invasion of Estonian territory. He and other senior officials from his government said that unknown assailants had come from Russia and abducted an Estonian security service officer at gunpoint, allegedly using smoke bombs and jamming the radios of Estonian border guards during the Friday morning raid.

Russia made no secret of its involvement. The security service known as the FSB (the post-Soviet incarnation of the KGB) told Russian news agencies that it had the officer in custody on suspicion of spying, but claimed he had been arrested on the Russian side of the border, not in Estonia. Given the timing, some Estonian officials saw the move as a blatant Russian provocation, not only against their country but the whole of NATO.

It is through such ambiguities that Russia has been testing NATO’s resolve, prodding and provoking to feel out the alliance’s weak spots. And it isn’t the first time Russia’s done this. During Estonia’s noisy 2007 spat with Russia over a Soviet war memorial, Russian hackers launched a massive cyberattack against Estonia that paralyzed the websites of its government, parliament, banks and media. Estonian officials blamed the Kremlin, and questioned whether a cyberattack of this or any other magnitude could trigger Article 5 of the NATO treaty. At the Wales summit this week the allies finally affirmed that it could, even suggesting that the NATO could launch a military response to a cyber threat. This seemed to patch a key hole in the alliance’s remit.

It is therefore both reasonable and rational for Russia, if it desires to pursue its territorial ambitions and to roll back NATO’s presence in Eastern Europe, to press the Atlantic Alliance’s commitment to collective defense. If Article 5 was invoked on behalf of a Baltic state and the major powers – America, France, Britain, etc. – failed to respond, the alliance would effectively dissolve. The integrity of the NATO alliance is already fraying at the edges in Anatolia. There, Turkey has elected to play both sides of the conflict in which a coalition of Western and Arab nations are engaged in a war against the Islamic State rebels. Turkey has essentially created a model whereby a NATO member state (that is not the United States) can ignore the security considerations of fellow allies.

Surely, Russia could miscalculate. It could engage in an act of aggression so momentous that it becomes impossible for the West not to respond with equal or greater force. If, however, the ongoing war in Ukraine is not an “invasion,” and it is not according to the White House, it is logical to fear that Russia has not yet received a clear signal as to what point its actions would trigger a military response.

That kind of ambiguity leads to parameter testing. Testing leads to miscalculation. And miscalculation often leads to war.