There had always been strong and widespread movements in the Warsaw Pact nations opposed to the regimes, and especially opposed to virtual occupation by the Soviet Union. Hungary in 1956, Czechoslovakia in 1967 and Poland in 1981 were the highlights, but the resistance existed below the surface during the Cold War. Even at the Politburo level, Gomulka's Poland was pushing for reforms as early as the 1950s.

Entering into 1989 - to address the OP's question directly - there was definitely a sense that things were changing especially in relations between the Americans and Soviets. Gorbachev was showing himself to be a new type of leader. Poland had their first free post-war elections (and the communists lost). [The contrast always struck me as iconic: the day Poland voted out the communists in free elections, the tanks rolled into Tiananmen Square]

What was different in 1989 was Gorbachev's statement the previous year that the Brezhnev doctrine was dead - Eastern European countries could decide their own futures. No longer would the Red Army step in and prop up regimes, as they had done in earlier rebellions. Gorbachev repeated his commitment to this position when he refused Erich Honecker's request to use the Red Army to put down German protest movements.

The 1989 revolutions were mostly the result of large-scale protest by the citizens of the Warsaw Pact nations. The people would protest, the governments would give a little bit of ground, the people would be inspired to protest more, and the cycle continued. This snowball effect is why so many regimes crumbled so quickly - protesters succeeding in Leipzig and Berlin inspired the people of Prague and Bratislava etc. Only in Romania did the state put up a fight, and that only lasted a few days and ended with the death of the President.

Hi! I was wondering the same thing a few months ago so I started digging deeper into what I know about the era. First of all, yes, even if only in retrospect. By 1988 Poland had already begun their transition some time ago, and migration across the room curtain was more prominent than before. Other signs became clearer later on however, as reformist governments were not yet in place in 1988. The speed of the fall is quite profound and many of the signs it might happen only became clear in the months before the opening of the Berlin Wall.

As for your second question, there are multiple reasons. The first being the mass migration from East Germany that caused pressure on Hungary, Czechoslovakia, and East Germany to change border policies. Many reforms came in the wake of small changes such as these. The next is that under pressure from the USSR, specifically Gorbachev, many bloc governments appointed reformist leaders like Mladenov in Bulgaria, Krenz in GDR, etc. My answer here is thin however because beyond this point the revolutions all played out in very individual ways with dissent led by different types of movements. Sorry this is shorter than most ask historians posts, I'm on mobile.

I'm running a project now actually to explore why the revolutions all played out at once, tweeting events of 1989 as they happened at @ironcurtainfall. My research for the project is helping me learn more about your question every day (and I cite sources once a week)

Surprisingly something I've spoken about in class extensively gets to be of use, even if it isn't my specialty!

First: Was there indication that revolution was on the horizon among outside observers?

My favorite source that answers both of these questions is by Timur Kuran, titled "Now Out of Never: The Element of Surprise in the East European Revolution of 1989". I'll cite it at the bottom in full. Essentially, it points out that there was no real prediction that the Soviet Union would fall apart, or communism would fall apart, when it did. People were stunned, even in the countries where revolution occurred. Even those who expected revolution in East Germany said they didn't expect it a peaceful revolution so fast, if at all. Only 5%, according to an Allensbach Institute survey in 1990, expected it to occur when it did (and this is subject to, as Kuran notes, the fallacy where people say they expected something when they didn't actually), while 18% said "yes, but not that fast". A full 76% said the revolution had totally surprised them.

It doesn't seem anyone really expected peaceful revolution, or revolution at all, when it happened. People who did expect revolution didn't expect the popular spontaneity, they expected things like war. And nobody knew when it would happen, even if they knew it probably would. Not even in 1988.

As for the follow-up, there are a lot of theories about it. Structuralists argue that the system is inherently untenable and that revolution is bound to happen in such a state structure, to make that basic. Voluntarist, rational choice theories argue that people free-ride on revolutions, fearing to put themselves in harms way. Eventually they presumably get fed up, but this doesn't really predict revolutions very well.

Kuran puts forward their own theory, based on an imprecise formula: people protest if their revolutionary threshold is reached, and this threshold being reached depends on their internal payoff (ie. breaking out of cognitive dissonance in supporting a regime they don't like), their private preferences (cost vs. benefits and dangers of revolt), and how many others protest. This crude and immeasurable formula suggests that when one nation rose up, the revolutionary thresholds of others were reached as well. If much of the public wants to protest, but there are only a select few who feel they have "nothing to lose" and have the spark to protest, they may ignite the rest of the public. If the regime represses people heavily, however, this may end up raising the revolutionary threshold for others, making the revolution sputter out and die (think China 1989, from my understanding of Tiananmen). So why did communist nations crumble? A mixture of:

• Lack of significant, heavy-handed repression by the Soviets, who had previously invaded countries seeking to reform or change their regime (Prague Spring, for example)

• Gorbachev's apparent attempts at rapprochement with the West signaled hopes for meaningful reform

• Economic promises that were not delivered and despised leadership were piling up for quite some time

• Gorbachev personally signaled the change anyways.

To elaborate some on that last point, when Gorbachev visited Finland (on October 25, 1989), he said (according to the NY Times the next day) that regional intervention was no longer proper. A quote from that NY Times Article:

His spokesman embroidered the theme jokingly, saying that Moscow had adopted ''the Sinatra doctrine'' in Eastern Europe. ''You know the Frank Sinatra song, 'I Did It My Way?' '' said Gennadi I. Gerasimov to reporters. ''Hungary and Poland are doing it their way.''

''I think the Brezhnev doctrine is dead,'' he added, using the Western term for the previous Soviet policy of armed intervention to prevent changes in the Communist governments of the Warsaw Pact, In talks with Finland's President, Mauno Koivisto, at the beginning of a three-day state visit, Mr. [Mikhail S. Gorbachev] was reported to have said that the current political upheavals in the East bloc must be allowed to run their course.

''The events that are now taking place in the countries of Eastern Europe concern the countries and people of that region,'' the Soviet leader told the Finnish President, according to Mr. Gerasimov, whose formal position is that of spokesman for the Soviet Foreign Ministry. ''We have no right, moral or political right, to interfere in events happening there. We assume others will not interfere either.''

There had been no repression, indications nothing would be interfered with, and all of the above. Some were pessimistic, of course. Kuran notes that the East Germans were still allowed to falsify local election results in 1989, and praise the Tiananmen Square Massacre by China, and Gorbachev didn't stop the East Germans from using force to disperse small demonstrations protesting these events. Still, Gorbachev's moves towards reform encouraged protest and made people more willing to take the risk, since they figured there was less risk involved. Even as East Germans protested, Gorbachev did not intervene and allowed the protestors to march when security forces did not fire on them or block them by force (on October 9, on October 7 crowds were attacked by police clubs while Gorbachev was in Berlin). And so it rolled and spiraled out of control.

Hope that helps!

Now Out of Never: The Element of Surprise in the East European Revolution of 1989 Timur Kuran World Politics, Vol. 44, No. 1 (Oct., 1991), pp. 7-48

I was in Leningrad in 1988 around October as a student for a few days, and stayed at the Pribaltiyskaya Hotel. Around the corner there was a bookstore that had a huge line stretching around the block. I asked a student-guy who tagged along with us (and I suspected was working for the tourist board). He said that they had just allowed Orwell's Animal Farm to be published and sold to the public. After hanging around with this guy, he told me about the videos from the West they watched on VCR. He asked me for a copy of the Monopoly game. The signs were there that the totalitarian state was crumbling. The celebration of the revolution was being toned down (according to the guy) and all the kids were listening to rock and watching movies like Rambo. Everyday people began to see that goods and life in the West were superior, and the party was distancing itself from Stalin. I have no sources, just my experience and one reference in Google books to the publication year in the USSR ( http://books.google.com/books?id=TG-YpkczTjEC&pg=PA166&lpg=PA166&dq=ussr+first+publication+of+Animal+farm+1988&source=bl&ots=jkl3jW2qB1&sig=YRqsy6-D8MfPagrlYuWopY6zceo&hl=en&sa=X&ei=X7ZxVMLXDrXOsQSQwoCgCg&ved=0CB8Q6AEwAA).

I don't have time to write a lengthy response here, but I'm in the Stephen Kotkin camp who views the fall of the Soviet system as essentially a revolution from above. The mass protest movement in bloc countries other than Poland and Romania has been highly exaggerated in Western media. A terrific book on this is: Stephen Kotkin. Uncivil Society: 1989 and the Implosion of the Communist Establishment. (New York: Random House, 2009).

Edit When I say "highly exaggerated" I mean to imply that it's difficult to weed out continuing anti-communist perspectives in many english history texts on Russian History. Kotkin provides a good non-biased neutral analysis.

Paul Kennedy's widely read and influential book The Rise and Fall of the Great Powers was published in 1989 and considers this very issue. The final chapter considers the fate of all the (then) great powers, including the Soviet Union. He identified many weaknesses; military, technological, demographic and, worst of all, systemic and economic.

He doesn't go so far as to say that the Soviet Union is on the brink of collapse... in fact, he twice emphasizes that we should not jump to this conclusion. However, the fact that he feels the need to say this twice in a relatively short section suggests that the idea is on his mind.

He does make one final interesting point... that none of the Great Power empires covered in his survey (Spain, Austria-Hungary, Ottoman or Britain) had retreated to an ethnic core without first having been engaged in a long, exhausting coalition war. We are fortunate that the Cold War managed to create the economic and systemic stresses to crack the system with relatively tiny amounts of actual bloodshed.

Relations in 1988 were warming up under Gorbechev and Glasnost which is Russian for increased openness and transparency and was a domestic social policy as well as a foreign one. In general people were at best cautiously optimistic that the cold war could some day end, maybe in a decade or so. Some thought it a ruse to get the west to reduce military spending. Almost nobody expected a collapse of the entire government. Nobody at all thought it would happen in less than a year and go from beginning to end so quickly. In hindsight it was inevitable to happen at some point. The Soviets spent way to much of their GDP in the arms race but couldn't keep up with western prosperity leading to more and more going to a military budget and less for its citizens. Keep in mind the Soviet Union was a managed economy so spending less on citizens led to massive shortages in everything. In the end far from being a ruse glasnost changed the way Soviet people viewed their government to such and extent they overthrew communism and its way of doing things altogether.

This news report of when East Germany announced it was opening its borders is interesting:

https://www.youtube.com/watch?v=jnCPdLlUgvo

I think this counts as a source in AskHistorians, at least to see what popular opinion was at the time. They use words like "astonishing" and "shockwaves" to describe what's occurring. A reporter on the ground in East Germany says, "This certainly wasn't anticipated in this form this quickly," and that while changes to travel restrictions were expected, "... the extent of the changes and the immediacy of them certainly were not anticipated at this time." When he asked a West German official if he expected a rush of people crossing the border he said, "I haven't the slightest idea."

People saw change coming, but did not anticipate the system to collapse so quickly and completely.