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Residents surround Soviet tanks in Prague on 21 August 1968 as the Soviet-led invasion by the Warsaw Pact armies crushed the so called Prague Spring reform in former Czechoslovakia. (Photo by - / AFP) (Photo credit should read -/AFP/Getty Images)

Residents surround Soviet tanks in Prague on 21 August 1968 as the Soviet-led invasion by the Warsaw Pact armies crushed the so called Prague Spring reform in former Czechoslovakia. (Photo by - / AFP)        (Photo credit should read -/AFP/Getty Images)

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File photo taken in August 1968 in Prague during confrontations between demonstrators and the Warsaw Pact troops and tanks, who invaded Czechoslovakia to crush the so called Prague Spring reform and re-establish a totalitarian regime. / AFP PHOTO / - (Photo credit should read -/AFP/Getty Images)

File photo taken in August 1968 in Prague during confrontations between demonstrators and the Warsaw Pact troops and tanks, who invaded Czechoslovakia to crush the so called Prague Spring reform and re-establish a totalitarian regime.
 / AFP PHOTO / -        (Photo credit should read -/AFP/Getty Images)

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Prague inhabitants pass next of two Soviet tanks standing guard in front of the entrance of Czechoslovak CTK press agency in Prague on 29 August 1968 as the Soviet-led invasion by the Warsaw Pact armies crushed the so called Prague Spring reform in former Czechoslovakia. AFP PHOTO / AFP PHOTO / CTK / LIBOR HAJSKY (Photo credit should read LIBOR HAJSKY/AFP/Getty Images)

Prague inhabitants pass next of two Soviet tanks standing guard in front of the entrance of Czechoslovak CTK press agency in Prague on 29 August 1968 as the Soviet-led invasion by the Warsaw Pact armies crushed the so called Prague Spring reform in former Czechoslovakia. AFP PHOTO / AFP PHOTO / CTK / LIBOR HAJSKY        (Photo credit should read LIBOR HAJSKY/AFP/Getty Images)

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File photo taken in August 1968 in Trutnov shows a tank as Warsaw Pact troops and tanks invade Czechoslovakia to crush the so-called Prague Spring reform and re-establish a totalitarian regime. (Photo by - / AFP) / The erroneous mention[s] appearing in the metadata of this photo by - has been modified in AFP systems in the following manner: [-in Trutnov--] instead of [-in Prague--]. Please immediately remove the erroneous mention[s] from all your online services and delete it (them) from your servers. If you have been authorized by AFP to distribute it (them) to third parties, please ensure that the same actions are carried out by them. Failure to promptly comply with these instructions will entail liability on your part for any continued or post notification usage. Therefore we thank you very much for all your attention and prompt action. We are sorry for the inconvenience this notification may cause and remain at your disposal for any further information you may require. (Photo credit should read -/AFP/Getty Images)

File photo taken in August 1968 in Trutnov shows a tank as Warsaw Pact troops and tanks invade Czechoslovakia to crush the so-called Prague Spring reform and re-establish a totalitarian regime. (Photo by - / AFP) / The erroneous mention[s] appearing in the metadata of this photo by - has been modified in AFP systems in the following manner: [-in Trutnov--] instead of [-in Prague--]. Please immediately remove the erroneous mention[s] from all your online services and delete it (them) from your servers. If you have been authorized by AFP to distribute it (them) to third parties, please ensure that the same actions are carried out by them. Failure to promptly comply with these instructions will entail liability on your part for any continued or post notification usage. Therefore we thank you very much for all your attention and prompt action. We are sorry for the inconvenience this notification may cause and remain at your disposal for any further information you may require.        (Photo credit should read -/AFP/Getty Images)

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File photo taken in August 1968 in Prague during confrontations between demonstrators and the Warsaw Pact troops and tanks, who invaded Czechoslovakia to crush the so called Prague Spring reform and re-establish a totalitarian regime. / AFP PHOTO / - (Photo credit should read -/AFP/Getty Images)

File photo taken in August 1968 in Prague during confrontations between demonstrators and the Warsaw Pact troops and tanks, who invaded Czechoslovakia to crush the so called Prague Spring reform and re-establish a totalitarian regime.
 / AFP PHOTO / -        (Photo credit should read -/AFP/Getty Images)