Aug 20
There was Prague
Not as bloody, but a similar stamping down of a green shoot of liberty.
The reforms, especially the decentralisation of administrative authority, were not received well by the Soviets who, after failed negotiations, sent thousands of Warsaw Pact troops and tanks to occupy the country. A large wave of emigration swept the nation. While there were many non-violent protests in the country, including the protest-suicide of a student, there was no military resistance. Czechoslovakia remained occupied until 1990.
I was young at the time and have no memory of it other than the period is often used as a setting for cold-war spy novels.