Russian servicemen look on as a Mi-24 helicopter fly overhead during the Open Water competition for pontoon bridge units, as part of the International Army Games 2018, outside Murom, Russia August 3, 2018. (Photo by Maxim Shemetov/Reuters)

A German rifleman beside the corpse of a French soldier in a trench at Fort Vaux, France, 1916. (Photo by Hulton Archive/Getty Images)

A man walks by as tourists take selfies on the French Riviera city of Nice on June 24, 2019, as temperatures soar to 33 degrees Celsius. Forecasters say Europeans will feel sizzling heat this week with temperatures soaring as high as 40 degrees Celsius (104 degrees Fahrenheit) in an “unprecedented” June heatwave hitting much of Western Europe. (Photo by Valery Hache/AFP Photo)

A moto-taxi driver takes two passengers past a burning barricade set up by people protesting fuel shortages in Port-au-Prince, Haiti, Monday, September 16, 2019. Haiti was at a standstill Monday with no public transportation available and closed banks, government offices, and schools amid street protests due to a fuel crisis. (Photo by Dieu Nalio Chery/AP Photo)

A member of the Palace staff arranges Queen Victoria's Stuart Ball costume which is part of an exhibition to mark the 200th anniversary of the birth of Queen Victoria (1819–1901) this year at Buckingham Palace in London, Tuesday, April 2, 2019. The exhibition, Queen Victoria's Palace at the Summer Opening of Buckingham Palace from 20 July – 29 September 2019, will tell the story of her 62-year reign and her life at Buckingham Palace, which began when she ascended to the throne in June 1837. (Photo by Frank Augstein/AP Photo)

Harris & Ewing Inc. photographed people, events, and architecture, particularly in Washington, D.C., during the period 1905-1945. Photo: Tests of Curtiss Palne for Army, Single Control. Created by Harris & Ewing. Published in 1912.

People look at a man, who residents said was killed by al Qaeda militants, hanging on a bridge in Yemen's southeastern city of Mukalla June 17, 2015. Al Qaeda militants in Yemen killed two alleged Saudi spies, residents said, accusing them of planting tracking devices which enabled the assassination of the group's leader in a suspected U.S. drone strike. (Photo by Reuters/Stringer)

In this Friday, December 5, 2014 photo, Iranian volunteer Asal Moghaddam plays with dogs at the Vafa Animal Shelter in the city of Hashtgerd 43 miles (73 kilometers) west of the capital Tehran, Iran. More than 500 dogs find care and affection at the Vafa Animal Shelter, which was established through an endowment in 2004 and is the country’s only licensed animal refuge. (Photo by Vahid Salemi/AP Photo)