I know that's the point, but it's wrong - nobody knew what the USSR was going to do in 1989. I know, I was living in Germany and marrying a Hungarian wife that year, and when the border guards in Hungary said to each other one fine summer day that it wasn't their job to keep vacationing East Germans bottled up away from Western Europe, and that if East Germany had a problem with that they could just come over here and say that, neener neener - none of that had anything to do with the USSR.
And aside from Romania, there weren't any dictators in the story. Hungary had had something like a Brezhnev figure in the 70's, but he was long gone by 1989 and there was just a Parliament. Same with East Germany - there was a Heimatssicherheitsamt (just a little joke there) but there was certainly no dictator.
And the crucial point is this - nobody knew that the USSR was going to wither up and blow away. This caused the USSR to wither up and blow away - it could very well have happened that the tanks would have rolled in by Christmas, but instead, the trucks rolled out and east.
In 1956, things worked exactly in this same manner - the people revolted, and only after a couple of months did the tanks roll in. (My mother-in-law was 10. She told me some stories. It will fry your American brain to realize your mother-in-law was playing next to stacked bodies one winter).
And actually in 1848 it was a similar situation.
Here, the expectation is that America's tanks will roll in - or at least their bombers will scream by overhead. They're not going to, though - and in that point, this wave is very, very much like 1989/90 in Europe. Each individual country has its own story. Some had people with their backs up against the wall, others just ... merged with their cousins.
To your second point - our own Revolution sparked off a few, France being one of them. And the European empires in Africa all fell within a few years of one another. When it happens, it changes maps.