I don't remember what I had imagined back then, so I'll say this:

It could've been ANYTHING, and WAS nothing. The "before it became dark in the galaxy" is a better case, because we can all relate to a state turning from a good kingdom, or a democracy, into an evil kingdom or reich or dictatorship from real life, but the "clone wars" bit was every bit as lacklustre and random as the PT's equivalent of "the oppression of the Sith".

The "prophecy" obviously gets at least two fat, large minus points for a) being a central plot point and b) retconning itself in the process of the trilogy.

It was just a cool sounding cliff note. That's all it was, and nothing in the rest of the series gave it any substance or basis for speculation.

Doesn't mean we can't try to make up cool, interesting ideas and what-could-have-beens, but in the movie, it was just that, an unnecessary cliff note in one expository line.

Couldn't the story instead been about Luke's father fighting against the evil empire and succumbing to the evil guys at the end? Why did they need to have some sort of separate "clone wars" in the backstory? Except, of course, the stormtroopers were clones, and the clone wars were where the Empire took over the Republic using... the clone troopers.

But hey, still a useless cliff note.