Czech language:

The languages have not undergone the deliberate highlighting of minor linguistic differences in the name of nationalism as has occurred in the Bosnian, Serbian and Croatian standards of Serbo-Croatian. However, most Slavic languages (including Czech) have been distanced in this way from Russian influences because of widespread public resentment against the former Soviet Union (which occupied Czechoslovakia in 1968). Czech and Slovak form a dialect continuum, with great similarity between neighboring Czech and Slovak dialects. (See "Dialects" below.)

Please answer a question about this article. If the question is unanswerable, say "unanswerable". When did the Soviet Union occupy Czechoslovakia?
1968