What was different in the '80s--what ushered in the era of superstar corporate raiders and then made it disappear forever--were the rise and fall of Michael Milken, and the hard knocks education of large institutional investors.
--From Dear Chairman: Boardroom Battles and the Rise of Shareholder Activism by Jeff Gramm
The otherwise exceptional book Dear Chairman gives QWT readers yet another example of how complex sentences and complicated writing inevitably hurts readers.
The sentence above is grammatically correct, although it sure doesn't seem so. In fact, it's the correctness of the grammar that makes it read poorly. Readers hiccup and lose their rhythm when they get to "were" after the second dash.
Why "were"? Because that verb's subject is plural: "Michael Milken" and "the hard knocks education of large instituional investors" were what was different in the '80s.
So, no problems with the grammar, but the sentence still needs help. It's confusing, it's unwieldly, and it reads like there's a grammar error even though there isn't. Do not fling sentences like this at your readers.
How can we fix it? Simplify it, make it direct... and omit needless words. Like this:
What was different in the '80s? The rise and fall of Michael Milken, and the hard knocks education of large institutional investors. This was what ushered in the era of superstar corporate raiders--and then made it disappear forever.