In this photo taken on Friday, July 14, 2017, a student at a paramilitary camp for children calls the rank to attention outside Kiev, Ukraine. As the deadly conflict in eastern Ukraine entered its third year, some parents in Ukraine are anxious to make sure their children are ready to fight it, instead of swimming and playing volleyball. (Photo by Efrem Lukatsky/AP Photo)

A reveller covered in tomato pulp takes part in the annual “Tomatina” festival in the eastern town of Bunol, on August 30, 2017. The iconic fiesta – which celebrates its 72nd anniversary and is billed at “the world's biggest food fight” – has become a major draw for foreigners, in particular from Britain, Japan and the United States. (Photo by Jaime Reina/AFP Photo)

A boy holds the remains of a mortar shell which hit a residential building in the village of Staromikhailovka, outside the separatist-held city of Donetsk, Ukraine, May 24, 2016. (Photo by Alexander Ermochenko/Reuters)

A cosplayer prepares before the start of the parade during the Metropoli (Media Culture and Entertainment Festival) in Gijon, northern Spain, July 3, 2016. (Photo by Eloy Alonso/Reuters)

South Vietnamese forces escort suspected Viet Cong officer Nguyen Van Lem (also known as Bay Lop) on a Saigon street February 1, 1968, early in the Tet Offensive. Moments later, Lem was executed by Gen. Nguyen Ngoc Loan, chief of the national police. (Photo by Eddie Adams/AP Photo)

Medic James E. Callahan of Pittsfield, Mass., gives mouth-to-mouth resuscitation to a dying soldier in war zone D, about 50 miles northeast of Saigon, June 17, 1967. Thirty-one men of the 1st Infantry Division were reported killed in the guerrilla ambush, with more than 100 wounded. (Photo by Henri Huet/AP Photo)

Revellers dressed in mock military garb take part in the “Els Enfarinats” battle in the southeastern Spanish town of Ibi on December 28, 2017. During this 200-year-old traditional festival participants known as Els Enfarinats (those covered in flour) dress in military clothes and stage a mock coup d'etat as they battle using flour, eggs and firecrackers outside the town hall as part of the celebrations of the Day of the Innocents. (Photo by Jaime Reina/AFP Photo)

A US Marine leads two Viet Cong suspects in restraints during the Tet Offensive on February 20, 1967. (Photo by Bettmann Archive/Getty Images)