Members of a teenage girl gang convincing an unwilling recruit to join the gang, circa 1955. (Photo by Vecchio/Three Lions)

An adult chimp plays with a young chimp at Chimp Haven in Keithville, La., Monday, February 18, 2013. One hundred and eleven chimpanzees will be coming from a south Louisiana laboratory to Chimp Haven, the national sanctuary for chimpanzees retired from federal research. (AP Photo/Gerald Herbert)

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

A German Shepard bares its teeth during Schutzhund attack dog training at Witmer-Tyson Imports February 14, 2002 in Newark, CA. (Photo by Justin Sullivan/Getty Images)

The hot air balloon “Hopper T Frog” from Park City, Utah, peeks over the red rock cliffs during the 23nd Annual Red Rock Balloon Rally at Red Rock State Park December 6, 2003 near Gallup, New Mexico. (Photo By Douglas Tesner/Getty Images)

Sam Warren climbs in to a prototype combat vehicle during the PrepperCon expo Friday, April 24, 2015, in Sandy, Utah. Hundreds of survivalists and “preppers” are gathering in the Salt Lake City suburb of Sandy for the first annual PrepperCon, featuring demonstrations of underground bunkers, food storage, and armored vehicles. (Photo by Rick Bowmer/AP Photo)

A soldier helps another with her ear protection at the Terningmoen Camp in Elverum, Norway on March 23, 2017. Soldiers demonstrate their skills and tactics during a contract drill as they train to become part of the world's first all-female special forces unit, the Jegertroppen or “hunter troops”. (Photo by Carolina Reid/NBC News)

These powerful images capture the spear-wielding tribes of Papua new Guinea who believe they are possessed with the spirit of the crocodile. They show how the Kangunaman clansmen scar their backs to resemble reptile scales while the Huli Wigmen wear elaborate headdresses to signal they are ready for battle. (Photo by Trevor Cole/Media Drum World)