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ZAGAN, POLAND - JUNE 18:  A soldier of the Polish Army mans a tank as a NATO flag flies behind during the NATO Noble Jump military exercises of the VJTF forces on June 18, 2015 in Zagan, Poland. The VJTF, the Very High Readiness Joint Task Force, is NATO's response to Russia's annexation of Crimea and the conflict in eastern Ukraine. Troops from Germany, Norway, Belgium, Poland, Czech Republic, Lithuania and Holland were among those taking part today.  (Photo by Sean Gallup/Getty Images)
ZAGAN, POLAND - JUNE 18:  A soldier of the Polish Army mans a tank as a NATO flag flies behind during the NATO Noble Jump military exercises of the VJTF forces on June 18, 2015 in Zagan, Poland. The VJTF, the Very High Readiness Joint Task Force, is NATO's response to Russia's annexation of Crimea and the conflict in eastern Ukraine. Troops from Germany, Norway, Belgium, Poland, Czech Republic, Lithuania and Holland were among those taking part today.  (Photo by Sean Gallup/Getty Images)

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What's the point of NATO?

Donald Trump has called it obsolete, and says that it has problems. But what is NATO, why is it important and what's its future? CNN's Nic Robertson explains.

What's the point of NATO?

Donald Trump has called it obsolete, and says that it has problems. But what is NATO, why is it important and what's its future? CNN's Nic Robertson explains.