Generally speaking, it was both, although the extent to which each part influenced the course of events varied from country to country. In general, the growing popular discontent with the economic stagnation and political ossification of the 1970s and 1980s coincided with a generational shift in the political elite in the late 1980s, as the "old school" Communist leaders died or retired due to old age and were replaced by a generation of younger, more reform-minded Communists. The most obvious example of this is the Soviet Union under Gorbachev, but there were similar processes throughout most of the Eastern Bloc as the older leaders stepped down: Erich Honecker in East Germany, Wojciech Jaruzelski in Poland, Gustav Husák in Czechoslovakia, János Kádár in Hungary, and Todor Zhivkov in Bulgaria. All of those countries underwent (relatively) peaceful transitions to non-Communist regimes by the early 1990s.

Note that I said "most" of the Eastern Bloc; Romania was the notable exception. Nicolae Ceaușescu's regime was the most resistant to reforms and the most reliant on its repressive apparatus (the Securitate) to maintain order; it's not surprising, then, that Romania was the only country which removed its Communist government through a violent revolution that led to the execution of its leader. It's probably the best case of popular pressure forcing the hand of the political elite, in this case through violent means. Ceaușescu had been something of a "maverick" within the Eastern Bloc since the late 1960s; initially this was welcomed in the West as he was the only leader to publicly oppose the Warsaw Pact invasion of Czechoslovakia in 1968, but later soured due to his determination in the 1970s and 1980s to resist reforms to the old Stalinist ways and his construction of a cult of personality that was unrivaled in the Eastern Bloc. All of the Eastern Bloc had experienced slow economic growth and shortages due to the inefficiencies of the command economy in the 1980s, but Romania was probably the most extreme example. Ceaușescu imposed harsh austerity policies in order to eliminate Romania's foreign debt, which included intensive exporting of food and consumer goods, leading to severe shortages and a declining standard of living in Romania. Obviously this led to growing popular discontentment with his regime, but the public's disapproval was held in check by the Securitate, which was the largest secret police force in the Eastern bloc relative to its country's population. He was subject to criticism from within the party, both for his failed economic policies and his abuses of human rights, but he was still re-elected as General Secretary in November 1989.

Even as the other Communist regimes crumbled around him, Ceaușescu remained determined not to change course in Romania. Protests started in Timișoara in December 1989 and spread around the country, as Romanians were aware of the events there and in the rest of Eastern Europe. The most famous image of the wave of popular resistance to Ceaușescu is the speech he gave in Bucharest just before Christmas, broadcast on national television, where the crowd turned against him and began jeering him and chanting slogans like "we are the people, down with the dictator". Riots spread through the streets of Bucharest and the military forces in the city defected to join the revolution. Ceaușescu and his wife were forced to flee the city by helicopter, but they were forced to land, arrested, and executed after a brief show trial on Christmas Day 1989. Ceaușescu was replaced by a group of Communist Party members who had opposed him from within the party, known as the National Salvation Front. Even in the country that had maintained the hardest of lines, the repressive instruments eventually fell apart due to popular resistance and forced a change of power at the top.

Source: Vladimir Tismăneanu and Sorin Antohi, Between Past and Future: The Revolutions of 1989 and their Aftermath (CEU Press, 2000)