Each year holds its security challenges, but 2014 was a roller coaster.

Russia invaded Ukraine, China ratcheted up tensions in the Pacific, ruthless Islamic State militants fighting in Syria used brutal tactics to seize ever larger chunks of the country before invading Iraq.

And in America, political gridlock continues to constrain US defense spending. Readiness has taken a beating as American forces remain engaged in Afghanistan, Iraq, Syria, across Africa, as well as increasing their presence in Asia to reassure worried allies.

Unrest around the world has driven the international community to respond. The question is whether their actions have been enough.

Defense News asked 15 leaders in military, government, academia and industry from Europe to Asia to the US to the Middle East for their perspectives about their region and how if fits 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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