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)

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)

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)

British soldiers inspect a captured German place in the Horseguards' Parade, London during World War I in November 1914, with the London Eye in the background as a reminder of just how much has changed in the last 100 years. (Photo by Peter Macdiarmid/Getty Images)

A Ka'apor Indian warrior (L) chases a logger who tried to escape after they captured him during a jungle expedition to search for and expel loggers from the Alto Turiacu Indian territory, near the Centro do Guilherme municipality in the northeast of Maranhao state in the Amazon basin, August 7, 2014. Tired of what they say is a lack of sufficient government assistance in keeping loggers off their land, the Ka'apor Indians, who along with four other tribes are the legal inhabitants and caretakers of the territory, have sent their warriors out to expel all loggers they find and set up monitoring camps in the areas that are being illegally exploited. (Photo by Lunae Parracho/Reuters)

A view of an entrance to the concrete case surrounding the pressure vessel of the reactor is seen inside the decommissioned Unit Six of the Greifswald nuclear power station outside Lubmin August 5, 2014. Unit Six was a part of East Germany's largest nuclear power plant that was nearly completed in 1990, when the country's re-unification halted construction. (Photo by Thomas Peter/Reuters)

Residents of the Korean port of Inchon surrender to American troops. (Photo by Bert Hardy/Getty Images). 1950