After the WWII, Czechoslovakia was liberated by Russia. Russian agents established strong political dominance, resulting in a coup of 1948. The totalitarian regime was swiftly established, leading to many political executions and natinalization.
Two decades after, socialist Czechoslovakia of late 1960s was slowly walking towards political reform and freedom of society. To prevent a loss of control and establishment of political plurality, Russia invaded Czechoslovakia on 20.8.1986 with force of 500 000 men and 6300 tanks.
The soldiers were told that the occupation is in fact protection of Czechoslovakia from an attack by NATO and were surprised by the resistance from the population. Among others, citizens were turning / hiding direction signs to slow down the movement of the army and later to protect the insurgents.
Soviet military remained until the fall of the Iron Curtain, strongly controlling Czechoslovakian government. The last Soviet soldiers left in 1991.