Since the fall of the Berlin Wall 25 years ago, war between two European states has been practically unimaginable. But Russia is now forcing the allies in the European Union and NATO to think the unthinkable.

There is no shortage of scenarios in which a comparatively "small" regional conflict in eastern Ukraine could turn into a global crisis. Russia could find a reason to openly intervene in Donetsk, in response to its desperate humanitarian situation, or the US could begin supplying Ukraine with weapons - or even directly intervene with airstrikes on rebel positions and be pulled into the crisis.

The partially rudderless discussion over how Ukraine can be effectively helped reflects NATO's helplessness. There is currently no security doctrine and no strategy to respond to this new threat from the East. Western politicians have reacted with consternation to the Kremlin's military show of force in the wake of the Ukraine crisis.

Dangerous maneuvers

Hardly a day goes by when Russian war planes aren't spotted over the Baltic Sea, flying in the airspace of the three Baltic - and EU - states. Some of these maneuvers have been extremely dangerous: the Russian military planes have a habit of turning off their transponders, rendering them invisible to civilian aircraft.

The list of serious incidents in the Baltic region is growing by the day. One day, an armada of Russian warships suddenly shows up off the coast of Lithuania, the next an unidentified underwater vehicle is spotted in Sweden's territorial waters. In response, Sweden now intends to call in additional reservists for military exercises.

Back to the Cold War

In recent months, the three Baltic states have placed weapons orders to the tune of more than one billion euros ($1.2 billion) - anti-tank systems in particular. In the early summer, Russian forces undertook large scale maneuvers not far from their borders. All of this has been accompanied by Russia's thundering rhetoric against Lithuania, Latvia, and Estonia.

All three countries are NATO members. Another NATO member further south, Romania, has also been on the receiving end of Moscow's military threats, as the Kremlin struggles for influence in the Romanian-speaking Republic of Moldova. Romania is now seen as a potential third flashpoint, after Ukraine and the Baltics.

Diplomatic ties between NATO and Russia were always thin. But even this thin thread has now been broken. One side no longer knows what the other is planning. As in the worst times of the Cold War, only intelligence reports and military assessments shape the image of the other side's defense capabilities and political intentions.

Europe: An uncertain continent

German Foreign Minister Frank-Walter Steinmeier recently commented: "We just talk about each other, not with each other." This new lack of dialogue is especially bad: in recent years, the system of conventional arms control has collapsed in Europe. Originally, NATO and Russia set out limits on conventional weapons in the Conventional Armed Forces in Europe Treaty, and agreed to mutual checks and regular meetings. But the CFE Treaty is now legally suspended and politically dead.

On the eve of a new year, Europe is an uncertain, unpredictable continent. Europe now urgently needs two things: a new security doctrine - and a political approach that will build its confidence.