For some time now, it has been acceptable to argue in polite company that a conflict between major powers is unlikely. Terrorism, state collapse, and ungoverned regions—all combined with the proliferation of weapons of mass destruction—constitute, in this consensus, the clearest and most present dangers to the security of America and the liberal world order.
How would a major power, theoretically led by rational actors, actually hope to achieve anything by military aggression against a peer, given that a major war is very likely to wreck the global economy, not to mention the devastating possibility than such a conflict could quickly escalate to involve WMDs? As noted military theorist Lt. Commander Ron Hunter once put the matter, "In the nuclear world, the true enemy is war itself."
Unfortunately, Vladimir Putin gives no evidence of accepting this consensus. His actions in Georgia and Ukraine have made clear that he is intent on re-establishing Russian supremacy in the "near abroad," and that he cares not one bit for the inconveniences of other countries' borders or international law. His aggressive bomber patrols and dry runs for the launch of nuclear cruise missiles indicate that he is willing to risk a fight with the NATO alliance. Putin's goal appears to be a very traditional one: the seizure of territory.
His method, on the other hand, has been adjusted for the realities of warfare in the nuclear (and information) age. Especially with the seizure of the Crimea, we have been provided a clear illustration of the script he is likely to follow as he turns his gaze to the next target—for example, the Baltic states.
Here is how to win a war in Europe in the early 21st century:
1) Create a paranoid atmosphere at home through a state propaganda campaign that legitimates your actions against the "fascists" and your efforts to protect countrymen who live under the thumb of foreign oppression.
2) Exploit fissures in the domestic politics of the major powers that oppose you.
3) Achieve strategic surprise when you strike.
4) Use local proxies in the area you are seizing to create a veneer of legitimacy.
5) Act quickly enough that your seizure of terrain establishes "facts on the ground" and thus presents the major powers with a fait accompli.
6) Threaten massive retaliation, including nuclear retaliation, if anyone tries to alter the facts on the ground you have just established.
7) Repeat as necessary.
It is in no way clear that Putin will feel the need to stop because he has reached the border of a NATO member. On the contrary, based on what we know about the man, it seems likely that Putin longs for the day he is able to destroy the NATO alliance, at least in the sense of being responsible for its collapse. Failing to entertain the possibility that he might attempt such a thing is wishful thinking, a failure of the imagination tantamount to the myopia that the 9/11 Commission argued was responsible for al Qaeda's success in 2001.
For an example of the kind of scenario that could come to pass in Europe, consider this essay by a pro-Ukraine writer named Thomas C. Theiner. Numerous caveats apply: Theiner presents an alarmist chain of events that is obviously at the extreme end of what Putin might attempt, his antipathy to Germany's political elite is similarly extreme, and the overall style of the piece inspires no great confidence that every technical detail presented therein is correct. Based on what we have seen in Georgia and Ukraine, I would expect any action Putin took against the Baltics to be more incremental than the scenario Theiner describes.
Yet what Theiner imagines—a Russian seizure of Estonia, Latvia, and Lithuania that relies on an assault on Sweden's Gotland Island—is well enough argued in its broad strokes to be a useful thought experiment. Putin rapidly seizes Sweden's lightly defended Gotland Island, informing the Swedish government that the invasion is merely temporary and to the end of protecting "Russian speakers in the Baltic States from 'fascist NATO aggression.'" The Russian military can then emplace what the military calls "anti-access/area denial" weapons (precision missiles, basically) in an advantageous spot in the middle of the Baltic sea where they are not vulnerable to the Polish military, as such weapons are in Kaliningrad.
By doing so, Russia makes reinforcing or resupplying the Baltic states from the sea extremely difficult. Then, as Theiner rather dramatically puts it:
But events on Gotland are just a minor blimp [sic] on this day, as at sunbreak Russian troops cross the borders of Estonia, Latvia and Lithuania to "free the people" of these three nations from their "fascist governments". ... By noon NATO ambassadors meet in Brussels. The ambassadors of the three Baltic States declare that their nations are under attack and request that article 5 [sic] is activated. Poland, the UK, Denmark, Norway, Canada, France, the US and a few others agree and want to give NATO’s Supreme Allied Commander Europe free rein to beat back the Russians and liberate the Baltic States. But Turkey, Greece, Germany and a few others refuse.
NATO is split, and a coalition of the willing, led by the U.S., the UK, and Poland, tries to help the Baltic states. But due to the Russian presence on Gotland and a refusal on Germany's part to cooperate, getting military assistance quickly to the Balts or to their neighbor Poland is no easy matter. Poland essentially stands alone.
Therefore, on the morning of the third day Russia issues a warning to Poland to cease fire, stating correctly that Russian forces have not entered Polish territory and therefore Poland should stand down and not risk having one or more of its city [sic] struck by a nuclear bomb for helping nations like Estonia, which have "greeted Russian forces as liberators".
In Theiner's nightmare scenario, Poland continues to fight and the Russians retaliate, destroying Łódź with a nuclear weapon. The United States and other powers, not wanting a full-scale nuclear war, do not respond. Russia consolidates its gains, having broken the NATO alliance and expanded the Russian empire.
This scenario is almost infinitely bolder and bloodier than anything Putin has attempted thus far. But the difference between what Theiner describes and what has already happened in Georgia and Ukraine is one of scale, not kind. What he writes is not, on its face, either impossible or risible, and it ought to keep men like NATO commander Philip Breedlove awake at night. European leaders have attempted similar things in the (recent!) past, and the hopes of John Kerry notwithstanding, the mere fact that we are in the 21st century does not constitute some sort of magic talisman that has ended war in our time.
Just ask the Crimeans.