Soviet Army soldiers sit on their tanks in front of the Czechoslovak Radio station building in central Prague during the first day of Soviet-led invasion to then Czechoslovakia on August 21, 1968. (Photo by Libor Hajsky/Reuters)

A military band prepares to play the national anthems before Cuban President Raul Castro welcomes U.S. President Barack Obama at the Palacio de la Revolucion in Havana March 21, 2016. Barack Obama on Sunday became the first US president in 88 years to visit Cuba, touching down in Havana for a landmark trip aimed at ending decades of Cold War animosity. (Photo by Jonathan Ernst/Reuters)

A schoolgirl runs past a burning barricade in Kibera slum, Nairobi on May 23, 2016 during a demonstration of opposition supporters protesting for a change of leadership ahead of a vote due next years. (Photo by Carl De Souza/AFP Photo)

A man demonstrates outside Republican presidential candidate Donald Trump's news conference at Trump Tower in New York, U.S., May 31, 2016. (Photo by Shannon Stapleton/Reuters)

Guanacos sit during a signing ceremony in Patagonia Park, Chile, January 29, 2018. Chilean President Michelle Bachelet signed decrees Monday creating vast new national parks using lands donated by U.S. conservation organization Tompkins Conservation in what is believed to be the largest private donation of land ever from a private entity to a country. (Photo by Esteban Felix/AP Photo)

A female goalkeeper saves the ball at the Mathare Environmental Conservation Youth Center during a soccer match to celebrate the International Women's day in Nairobi, Kenya, March 8, 2017. (Photo by Thomas Mukoya/Reuters)

Russian servicewomen march at Red Square during the Victory Day military parade in Moscow on May 9, 2017. Russia marks the 72nd anniversary of the Soviet Union's victory over Nazi Germany in World War Two. (Photo by Kirill Kudryavtsev/AFP Photo)

Tourists walk as others relax on the beach in the Red Sea resort of Hurghada, Egypt, July 17, 2017. (Photo by Gleb Garanich/Reuters)