NATO's response has been firm. We are making our forces more agile and able to respond swiftly and firmly, whenever and wherever new threats arise. We already have an increased presence in the air, at sea and on the ground in the eastern part of our alliance. And we are developing a very-high-readiness "spearhead force" able to deploy within a few days.

ABOUT THIS SERIES: Defense News asked 15 thought leaders in military, government, academia and industry -- from Europe to Asia to the US to the Middle East -- for their perspectives on their region and how they fit into world events. The result is a comprehensive collection of viewpoints that puts 2014 into context while forecasting the challenges -- and what must be done to meet them -- in 2015.

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The aim is to reassure our own allies and to deter anyone who might wish to threaten us. That's why we also want to ensure that we effectively address the challenges posed by the "hybrid warfare" we have seen in Ukraine, including how to deal with covert threats and provocations that fall below the threshold of a direct armed attack.

See the other contributors to "2015 Outlook."

At the same time, we are also looking south. Dealing with the Islamic State demands a comprehensive effort, including military, political and economic measures, and allies welcome the fact that the United States is leading a broad coalition effort. While the military campaign is not a NATO operation, all NATO allies are playing their part, along with Middle Eastern partners whose forces are interoperable thanks to years of working alongside NATO.

In the coming year, NATO will stand ready to strengthen the defense capacity of Iraq, Jordan and other partners in the region. We are working to further enhance interoperability with partners across the globe. But there should be no doubt that we will defend ourselves against any new threats, whether emanating from the east or the south.

Keeping NATO strong will require effort and commitment, but also adequate resources. NATO leaders have pledged to reverse the decline in their defense spending, and to increase spending in real terms over the coming decade. But fulfilling that pledge will be a challenge for many allies (and a few are at risk of backsliding already).

Even if overall defense spending grows in the coming years, budgets will remain tight. And so delivering the necessary forces and capabilities will require more substantial multinational defense cooperation — what we call Smart Defense.

To succeed, we need a closer NATO-industry partnership, one that encourages greater involvement by defense firms on both sides of the Atlantic in the early stages of developing the capabilities we need. And we also need greater collaboration and complementarity between NATO and the European Union in this area.

NATO and the EU share 22 common members, common values and common interests. We need to work together in developing military capabilities and industrial standards. But we also need to combine our efforts in shoring up the sovereignty and resilience of our common neighbors, like Ukraine, and in maintaining a united front against Russia's unacceptable behavior.

In these uncertain times, a strong NATO is a powerful source of stability. But it will require that all 28 allies pull their weight, and that the United States continues to demonstrate the leadership and engagement it has shown since NATO's creation 65 years ago.

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