US marines
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US marine: 'I am not worried about going to war'

14 January 2014 Last updated at 18:52 GMT

Across the globe there are men and women fighting in many conflicts.

In the US, serving in the military is a way for young people to get a subsidized university education.

The BBC's Regan Morris went to San Diego to meet with an 18-year-old marine to ask him why he joined the military.