US Defence Minister James Mattis greets officials as he attends a NATO defence ministers meetings at NATO headquarters in Brussels on February 15, 2017 | Emmanuel Dunand/AFP via Getty Images Opinion NATO survival will depend on Germany Europe is $100 billion short of strategic autonomy. Berlin could close that gap.

The United States will meet its commitments in Europe but NATO's European members have to step up on their defense spending — that's the message U.S. Defense Secretary James Mattis will try to hammer home when he meets with European counterparts in Brussels.

What we're not likely to hear is that the answer to the alliance's spending woes largely hinges on just one country: Germany.

With Europe's largest GDP and by far its strongest economy, Germany is the swing state in European defense. If Berlin commits to spending the recommended 2 percent of GDP on defense, it would add $30 billion of defense spending in Europe — a large share of the $100 billion surplus that would be generated if all European members and Canada met their targets. The move would significantly boost European defense.

On the flipside, marginal increases from Berlin — along the lines of what it has done since 2014 — would keep European defense spending stuck between 1.2 and 1.3 percent of GDP, an embarrassingly low average considering Europe’s share of global GDP is larger than the Americans'.

The question, however, is whether Germany can — or indeed should — become the leading military power in Europe.

German leaders are well aware of their NATO allies' expectations even if they are not always publicly expressed. Despite Berlin's initial resistance to sign NATO's defense pledge, its defense budget has increased every year since 2014. The German defense ministry has secured some hard-won increases from Finance Minister Wolfgang Schäuble, the keeper of Germany’s austerity budget, and Chancellor Angela Merkel has repeated on many occasions her commitment to increase defense spending.

But behind the encouraging statements, Germany only allocates a disappointing 1.2 percent of GDP to defense. The Bundeswehr is underperforming and has a limited ability to deploy its own troops or those of its allies. Germany is one of the world's leading defense manufacturers and exporters, but too much of its defense budget is apportioned to personnel spending. No wonder, then, that German pledges to increase spending are usually met in Paris with an ironic shrug that it will only serve to make German officer pensions more attractive.

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Getting Germany to punch closer to its weight will not be easy. Berlin's next coalition in the Bundestag will have to break with two powerful dogmas of post-World War II Germany: a balanced budget and a pacifist mindset.

Both ideas are deeply entrenched in Germany's political culture and institutions. But should Merkel be reelected and commit to greater military spending, it would not be the first time the pragmatic chancellor instigated a radical shift with incremental steps. Just look at her refugee policy or her firm stance against Russia, which clashes with major German industrial interests and coalition partners.

Germany's postwar doctrines are not as intractable as they seem. One of Merkel's own predecessors, Konrad Adenauer, already partly broke with one when he decided to rearm Western Germany against the advice of many in his own party in the early 1950s.

Some European politicians and security experts have indulged in wishful thinking that Donald Trump's presidency could mark Europe's chance to assert itself as a more autonomous power. But the numbers tell another story.

Europe is $100 billion short of strategic autonomy. A recent closed-doors exercise with former top officials from the Pentagon and U.S. military as well as senior European officials revealed that neither side could properly defend Europe from Russian hybrid attacks. The U.S. is over committed globally and, in the best case, will only commit to a marginal increase of spending in Europe. The Europeans still lag behind in terms of modern warfare capabilities.

Now more than ever, $100 billion is a long shot. Other important European players — such as Italy, Spain and the Netherlands — are either too small or too economically weak to have much of an effect on the European defense balance. In this scenario, Germany's $30 billion could make all the difference between a stronger Europe or a weaker one.

Short of that, any talk of a European defense union, or even of a European pillar within NATO, will remain just that — talk.

Fabrice Pothier is senior associate at Rasmussen Global and non-resident senior fellow at the Brent Scowcroft Center on International Security at the Atlantic Council, Washington, D.C. He was formerly head of policy planning at the office of NATO’s secretary-general.