Soldiers, including two recruits who have brought some chickens, at Victoria prepare to board the train for the battle front. (Photo by Hulton Archive/Getty Images)

A recruitment drive during the First World War at Trafalgar Square, London. (Photo by Central Press/Getty Images)

Military helicopters fly in formation above a billboard with a picture of China's late Chairman Mao Zedong during a training session for the upcoming parade marking the 70th anniversary of the end of World War Two, on the outskirts of Beijing, July 2, 2015. Troops from Russia and Mongolia will march together with Chinese forces in a parade in Beijing in September to commemorate the end of World War Two, the government and state media said on Thursday, confirming the first two foreign participants. (Photo by Jason Lee/Reuters)

Star Wars fan Mike Deguzman practices with a toy lightsaber after purchasing some new toys that went on sale at midnight in advance of the film “Star Wars: The Force Awakens” in Times Square in the Manhattan borough of New York, September 4, 2015. (Photo by Carlo Allegri/Reuters)

Cristine Angelie Garcia (C), 24, rides a jeepney on her way to work at a call centre for the midnight shift in Taguig city, Metro Manila, Philippines October 3, 2016. “Maybe there is another way where people do not need to die”, she said, adding she felt safer walking the streets at night. “I'm on Duterte's side. Maybe he's just misunderstood because he grew up on the streets”. (Photo by Ezra Acayan/Reuters)

A man holds a cow at the cattle market in Maiduguri, Nigeria, March 9, 2016. A Nigerian government push to strangle the Boko Haram insurgency has shut down the cattle trade that sustained the city of Maiduguri, leaving many residents with no livelihood, including many of the two million people displaced by the war. In recent months the army has taken back much of the territory lost to the jihadists during the five-year insurgency. (Photo by Afolabi Sotunde/Reuters)

Canadian soldiers from the Royal 22nd Regiment take up a position during a non-combative extraction operation in a simulated village as part of Rim of the Pacific (RIMPAC) 2016 exercise held at Camp Pendleton, California United States, July 11, 2016. (Photo by Mike Blake/Reuters)

“Shortly after he arrived, Van Agtmael witnessed the aftermath of this suicide bombing at a cafe that soldiers frequented in Mosul. Nine people died and 23 were wounded”. (Photo and caption by Van Agtmael/Harrison Jacobs/Magnum Photos)