In 1956, students took to the streets to protest about their lack of political freedom under soviet rule. This led to in the capital Budapest, police clashed with the protesters.
Krushchev sent the army into Hungary to restore order. he replace communist dictator Rakosi with more liberal Imre Nagy. the army then withdrew
At the end of October 1956, Nagy announce the withdrawal of the Warsaw Pact and became a neutral country, and a degree of sharing with non-communist groups. This gave Khrushchev serious cause of concern. if hungry broke away from the Warsaw Pact others might follow