Excerpts from Books and Wikipedia
"The invasion of Czechoslovakia by a Soviet-lead coalition brought to an end the Prague Spring, a period of liberal reforms by the Czech government of Alexander Dubcek. . . . The tragedy was that Dubcek did not understand how reforms in Czechoslovakia impacted the communist world. In Poland there were demonstrations demanding similar reforms. Moscow feared such agitation could spread to the Ukraine. . . . The West denounced the invasion, but took no action. Within the communist world a clear message was received. Real change and communist rule were incompatible." [Furtado: 1001 Days]