As Russian forces begin exercises on Ukraine’s border and continue their hold on Crimea, I worry about military escalation—unintentional and intentional. What fuels my concern about unintentional escalation is a disconcerting interaction I had last year with a Russian general at a NATO conference in Europe. I was leading a breakout session with a dozen generals and admirals from the region. I was taken aback as many of the Western European NATO officers began lamenting their individual countries' declining defense budgets and their inability to keep up with American military capability. As complicated as things might be inside NATO, and as difficult as it is to rally collective action at times, NATO is still the premier military alliance in the world. No one is giving up on it, I assured them.

When the Russian general spoke, he leaned into the table and said, "When I was a young soldier in the Soviet Army during the Cold War, I thought of NATO like this..." and he held his hand into a powerful fist. "But now that I am serving with NATO as a liaison, I am thinking, this..." and his hand went limp and wobbly with a whiny sounding sigh. If this small interaction reflects in any way a wider view of NATO by Russian civilian and military leaders, NATO has its work cut out for it in demonstrating to Vladimir Putin that continued military aggression in Ukraine will be challenged.

It is perfectly reasonable to want to avoid military confrontation with Russia. But deterrence requires a credible threat of military action. The various economic and diplomatic efforts to isolate Russia and compel Putin to pull back his troops are wise, and they are likely to have an effect. But soft and hard power are two sides of a coin. We need to recognize how military options fit into this strategy.

Putin has already provoked the region militarily by taking Crimea and now aggressively positioning more forces near the Ukraine border. The threat of further escalation against greater Ukraine is clear. However uncomfortable it may be to contemplate military action, not contemplating it and projecting that fact to one's adversary, would be the opposite of deterrence.

Militarily and politically, it would be unwise for Putin to push further into Ukraine. At a minimum, the farther west his troops go, the more Ukrainian resistance they will encounter. Assuming Russia is able to quickly defeat Ukraine's much smaller military, Putin must know that securing this victory and occupying greater Ukraine will require a complex counterinsurgency-like operation of uncertain duration that in the end may not be worth the cost. Still, the less resistance Putin perceives he might meet in that initial drive, the more likely he might risk it. The task for NATO, therefore, is to instill a healthy dose of uncertainty about what kind of military might he may encounter if he continues his march beyond Crimea and into Ukraine.

So it is welcome news that the U.S. is responding to requests from Eastern European NATO allies to send more fighter planes to the Baltics. But there is more we can do now to assure allies and deter, without necessarily provoking, Putin. For instance:

● Place NATO forces, such as the quick reaction force and America's 173rd Airborne in Italy on alert;

● Start NATO contingency planning for humanitarian spillover or worse;

● Position NATO warships in the Black Sea;

● Offer military assistance and advice to the Ukrainian military who should be planning the military defense of their country;

● Position reconnaissance assets (space, cyber, drone) to monitor escalation.

It is an uncomfortable reality that avoiding military escalation sometimes requires overt military countermoves. In this case, such moves will assure allies and partners in the region and send a powerful message that NATO's Article 5 guarantee (and also America's security guarantees beyond the region) still mean something. Hopefully they will deter Vladimir Putin from greater aggression; but if not, they will position forces in a way that provides NATO leaders more options to aid Ukraine and prevent greater spillover should the situation deteriorate. As Putin contemplates expanding his reach beyond Crimea and into Ukraine, he needs to understand that there will be consequences from all elements of NATO, Europe, and US power.

Janine Davidson is senior fellow for defense policy at the Council on Foreign Relations. From 2009 to 2012, she served in the Obama administration as the Deputy Assistant Secretary of Defense for Plans. She began her career as a United States Air Force cargo pilot, flying combat support and humanitarian missions in Asia, Europe and the Middle East.