Tactics reminiscent of the early American frontier days are now being used in Vietnam. Lieutenant Commander Donald D. Sheppard, UBN, of Coronado, California, aims a flaming arrow at a bamboo hut concealing a fortified Viet Cong bunker on the banks of the Bassac River, Vietnam on December 8, 1967. (Photo by AP Photo)

US marines watch the mushroom cloud from an atomic explosion rise above the Yucca flats, Nevada during a US nuclear weapons test. (Photo by Keystone/Getty Images). USA, 1945

Spacewalker Mark Vande Hei took his own photograph during the first spacewalk of 2018, on January 23, 2018. These sky-high pictures are better known as “space-selfies”. (Photo by Mark Vande Hei/NASA)

An undated handout image provided by UNICEF Germany on 20 December 2016 shows the “UNICEF Photo of the Year 2016” by Iranian freelance photographer Arez Ghaderi. Ghaderi won the first prize for his picture of a girl in a makeshift tent city in the Razavi Khorasan province, Iran, it was announced at a ceremony in Berlin, Germany on 20 December 2016. (Photo by Ariz Ghaderi/EPA/UNICEF Deutschland)

Local priests celebrate the “Aimara New Year”, an Andean Bolivian traditional festival that marks the winter solstice in El Alto, Bolivia, 21 June 2016. Aimara or Aymara means the Return of the Sun. (Photo by Martin Alipaz/EPA)

In this April 13, 2018 photo, motorcycle taxi driver Ricardo Medina, 60, transports vegetable vender Rigoberto Herrera Mendez, left, and coconut vendor Osvaldo Ochoa in Campo Florido, east of Havana, Cuba. The three men expressed hope that new government leadership will improve things, saying the country cannot move backwards. “We survive life with our work”, said Medina. (Photo by Ramon Espinosa/AP Photo)

Audience take photos of a model presenting a creation by Greek designer Dimitrios Ordoulidis during the 10th Athens Exclusive Fashion Week in Athens, Greece, October 22, 2016. (Photo by Alkis Konstantinidis/Reuters)

Siberian Husky dogs of the Royev Ruchey Park team pull a rig during a practice session for the Karadag Sled Dog Rally on the frozen Mana River, with the air temperature at about minus 21 degrees Celsius (minus 5.8 degrees Fahrenheit), in the Siberian Taiga area outside Krasnoyarsk, Russia February 6, 2018. (Photo by Ilya Naymushin/Reuters)