A Romanian honor guard soldier stands still as three military aircraft carriers are crossing the sky during a ceremony held at the Unknown Soldier Memorial, in Carol I Park, on the occasion of the Heroes' Day commemoration, in Bucharest, Romania, 10 June 2021. (Photo by Robert Ghement/EPA/EFE)

An Iraqi special forces soldier shot dead an Islamic State suicide bomber in Mosul, Iraq March 3, 2017. (Photo by Goran Tomasevic/Reuters)

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

Israeli soldiers get ready to launch the Skylark drone during a drill on January 16, 2012 near Bat Shlomo, Israel. (Photo by Uriel Sinai/Getty Images)

Taliban soldiers ride bumper cars at an amusement park in Kabul, Afghanistan on September 13, 2021. (Photo by WANA via Reuters)

An American soldier walks ahead of an MKIV (Mark IV) British-made tank, circa 1918. (Photo by Hulton Archive/Getty Images)

A soldier eats ice cream as she visits a zoo in Pyongyang, North Korea, September 12, 2018. (Photo by Danish Siddiqui/Reuters)

A soldier walks on the bank of the river in central Pyongyang, North Korea on April 16, 2017. (Photo by Damir Sagolj/Reuters)