Nicolae Ceausescu set up a very unstable communist regime in 1965, using a secret police to destroy opposition and scare civilians into obedience. Even then, opposition grew.
Ceausescu's awful economic policies led to huge amounts of famine, leading to rations of various items. His urbanization plan called for dramatic changes in lower class life, such as the relocation of entire towns and villages. This enraged Romanians further.
After the murder of thousands of women, children and men by Ceausescu's secret police, the people and army of Romania had had enough. The army stopped supporting anymore repression, and eventually Ceausescu was captured. He was executed Christmas Day. A new government was quickly formed after.