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 participant covered in coloured powder gestures as she stands near a Syrian army soldier during “I Love Damascus” marathon at Umayyad Square in Damascus, Syria October 7, 2016. (Photo by Omar Sanadiki/Reuters)

Guests brew coffee during a wedding ceremony for a Free Syrian Army fighter in the town of Douma, eastern Ghouta in Damascus, Syria January 19, 2016. (Photo by Bassam Khabieh/Reuters)

A Free Syrian Army fighter walks past a flag of al-Furqan brigade as a rifle hangs from a branch in the orchards of Kafar Zita in Hama countryside January 22, 2015. (Photo by Mohamad Bayoush/Reuters)

A fighter belonging to Jaish al-Islam (Islam Army) runs to take cover near the frontline on March 14, 2016 in the neighbourhood of Jobar, on the eastern outskirts of the capital Damascus. (Photo by Amer Almohibany/AFP Photo)

A visitor poses for a photograph in front of a 3D painting depicting a Japanese Imperial army soldier at a 3D art gallery in Beijing January 16, 2015. (Photo by Kim Kyung-Hoon/Reuters)

Ethnic Wa performer dressed as United Wa State Army (UWSA) soldiers perform a traditional dance in Mongmao, Wa territory in northeast Myanmar October 1, 2016. (Photo by Soe Zeya Tun/Reuters)

In this photo made late Saturday, August 9, 2014, in Keelung, Taiwan, a traditional Chinese dance troupe performs during a parade marking the beginning of the Chinese folklore's mid-summer's Ghost Month Festival. Fourteen days into the seventh month of the lunar calendar, August 9, in 2014, marks the traditional Chinese Ghost Month where the gates of the underworld are opened and spirits of the deceased are set free to roam the world of the living. The month long festivities are aimed to please the roaming spirits. (Photo by Chiang Ying-ying/AP Photo)