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)

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)

A dejected German Grenadier carrying a machine gun on his shoulder in front of a building on fire during the German retreat in Russia. (Photo by Keystone/Getty Images). 1944

German field telegraph operators at work in Warsaw. (Photo by Hulton Archive/Getty Images). 1st October 1914

Russian soldiers write home while serving on the Eastern Front during World War I, circa 1915. (Photo by Hulton Archive/Getty Images)

Actor Brad Pitt films a scene from “World War Z” in Glasgow City centre on August 18, 2011 in Glasgow, Scotland. The film, which is set in Philadelphia, will be shot in various parts of the city transforming it into ruins to shoot a post apocalyptic zombie film. (Photo by Jeff J Mitchell/Getty Images)

A ship being used for the filming of World War Z sets sail from Falmouth Harbour on August 4, 2011 in Falmouth, United Kingdom. The Cornish coastal town is currently being used to film the zombie film that stars Brad Pitt. (Photo by Matt Cardy/Getty Images)