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)

Newborn giant panda triplets, which were born to giant panda Juxiao (not pictured), are seen inside an incubator at the Chimelong Safari Park in Guangzhou, Guangdong province August 9, 2014. According to local media, this is the fourth set of giant panda triplets born with the help of artificial insemination procedures in China, and the birth is seen as a miracle due to the low reproduction rate of giant pandas. (Photo by Reuters/China Daily)

The first tram is delivered to the Gogar tram depot on October 17, 2011 in Edinburgh, Scotland. The tram was delivered on a low loader which had driven from Irun, northern Spain and is the first of 27 trams expected to arrive at the depot over the coming months. Last month the Scottish Government intervened to oversee the troubled Edinburgh trams project assigning project managers from Transport Scotland to work with contractors Bilfinger Berger. (Photo by Jeff J Mitchell/Getty Images)

A Syrian youth Khaled from Raqqa walks on snow wearing slippers in the Bekaa Valley refugee camp in Lebanon after the first heavy snow storm hit Lebanon, January 3, 2016. (Photo by Jamal Saidi/Reuters)

Riot police walk in the street as a couple kiss on June 15, 2011 in Vancouver, Canada. Vancouver broke out in riots after their hockey team the Vancouver Canucks lost in Game Seven of the Stanley Cup Finals. (Photo by Rich Lam/Getty Images)

Battle-weary American troops withdraw from Yong San in Korea. (Photo by Keystone/Getty Images). 1950