On the evening of November 15, German Chancellor Angela Merkel was driven in a white BMW to the Hilton Hotel in downtown Brisbane, the capital of the Australian state of Queensland.

While other leaders of the G20 group of leading economies were finessing the final communiqué of their summit, Merkel went on to spend four hours in the hotel with Russian President Vladimir Putin to discuss the Ukraine crisis.

Their respective foreign policy advisers - Merkel's Christoph Heusgen and Putin's Yuri Ushakov - were not admitted, nor were note takers or interpreters. Merkel has fluent Russian, Putin fluent German. Jean-Claude Juncker, the European Commission president, joined the discussion halfway through.

This was Merkel's second lengthy meeting with Putin in just four weeks. On October 17, she met him in Milan. That yielded no results. Putin was not willing to give up eastern Ukraine.

Between Milan and Brisbane, three things have happened that are bound to have a serious impact on European security and the EU's strategy toward its Eastern neighbors.

The first is that on November 12, NATO reported that Russia had sent in military convoys to the pro-Russian rebels in eastern Ukraine, which Russia denied. There is now a consensus that the fragile ceasefire agreed to between Ukraine, Russia, the rebels, and the Organization for Security and Cooperation in Europe in Minsk on September 19 is in tatters. Russia is again on the offensive in eastern Ukraine.

Second, it became clear that Europe faces the prospect of a long standoff with Putin. Just consider Russia's many incursions into the Baltic states' airspace over the past few weeks. It's as if Moscow is testing NATO's resolve to defend its allies. If so, the conflict is becoming a dangerous battle of wills between NATO and Russia.

As it is, Russia's invasion of eastern Ukraine has undermined Europe's post-Cold War security architecture. Those security structures were based on a cooperative relationship with Russia. That partnership no longer exists. European leaders will have to deal with that reality sooner rather than later.

The third significant event is that at the G20 summit in Brisbane, Russia earned the wrath of Japan and Australia, which shows that criticism of the Kremlin is not confined to North America and Europe.

Tokyo and Canberra are disgusted over Russia's attitude toward the (almost forgotten) downing of Malaysia Airlines flight 17. Along with the United States, Australia and Japan signed a joint statement in the margins of the G20 summit in which they condemned Russia's position.

"The three leaders resolved to tackle pressing issues such as . . . opposing Russia's purported annexation of Crimea and its actions to destabilise eastern Ukraine, and bringing to justice those responsible for the downing of Flight MH17," according to the statement.

Indeed, the criticism by G20 leaders of Putin's actions was so unremitting in Brisbane that he left the summit early. He said he needed sleep because he had to work on Monday morning.

The question now is what to do with such unity. Much depends on Merkel.

Merkel is not willing to give Putin the chance to save face, which some European diplomats and leaders might like to get the Ukraine dossier off their desks. She simply does not trust him. Merkel's 38 telephone conversations with Putin have only deepened that mistrust.

Her concern is not only about Ukraine or about Russian meddling in Armenia, Georgia, and Moldova. Merkel's efforts to persuade Putin to exert some influence over Syrian President Bashar al-Assad have also come to naught. To this day, Russia continues to supply weapons to Syria and support its leader unequivocally. So much for Berlin and Europe believing that Russia is an indispensable partner for resolving other crises.

Yet because Merkel has been the West's indisputable interlocutor with Putin, she is saddled with one of her biggest foreign policy and security challenges since becoming chancellor nine years ago.