Czechoslovakia was a country in Eastern Europe. Its capital city, Prague, was visited by the Doctor in most of his incarnations. (PROSE: Life from Lifelessness, Spoilsport, The Dragons of Prague, Suspension and Disbelief, Leap Second, Sunday Afternoon, AD 848,988, Fable Fusion, War in a Time of Peace; COMIC: The Broken Man)
After her defection from the Soviet Union to the United Kingdom in 1958, the Czech scientist Nadia Červenka provided the Sen-Gen Facility with a neuro-chemical hallucinogen developed using a yellow fungus which was discovered in the Tunguska crater. It was believed to be extraterrestial in origin. (AUDIO: Artificial Intelligence)
It was under the influence of the Soviet Union until 1989, when average people successfully campaigned for democratic rule. According to the Eleventh Doctor, the Czech communist government resigned between November and December 1989. The Doctor, Amy Pond and Rory Williams were present in Prague in November 1989 to witness the last gasps of that oppressive regime.
The Doctor claimed, however, that the fall of communism in Czechoslovakia was not at a fixed point in time, and so the time travelling trio had a genuine part to play in the success of democracy in the country in 1989.