A German rifleman beside the corpse of a French soldier in a trench at Fort Vaux, France, 1916. (Photo by Hulton Archive/Getty Images)

A South Sudanese People Liberation Army (SPLA) soldier patrols the streets in Malakal on January 21, 2014. (Photo by Harrison Ngethi/AFP Photo)

Romanian soldiers take part in a joint military exercise with NATO members, called “Agile Spirit 2015” at the Vaziani military base outside Tbilisi, Georgia, July 21, 2015. Georgian soldiers along with U.S. marines and platoon-size units from Bulgaria, Latvia, Lithuania and Romania are taking part in the exercises at the Vaziani military base outside Tbilisi. (Photo by David Mdzinarishvili/Reuters)

A Saudi soldier fires a mortar towards Houthi movement position, at the Saudi border with Yemen April 21, 2015. (Photo by Reuters/Stringer)

Three Chinese soldiers at the time of a civil war in China. (Photo by General Photographic Agency/Getty Images). 1922

A line of soldiers firing handguns during a training session, circa 1920. (Photo by Keystone). P.S. All pictures are presented in high resolution.

Soldiers take part in a drill during a heavy snow in Heihe, Heilongjiang province, February 26, 2014. (Photo by Reuters/China Daily)

U.S Army combat camera photographer Spc. Hilda Clayton took this photo July 2, 2013 that was released by the U.S. Army, that shows an Afghan soldier engulfed in flame as a mortar tube explodes during an Afghan National Army live-fire training exercise in Laghman Province, Afghanistan. The accident killed Clayton and four Afghan National Army soldiers. (Photo by Spc. Hilda Clayton/U.S. Army via AP Photo)