The Younger Dryas Boundary Event basically fucked humanity over, we really could have used a few more millennia of social and scientific development before we resorted to authoritarian agricultural civilization. Slavery, theistic religion, blood sacrifice, totalitarianism are all products of the plow becoming a necessity before we understood anything.
Constantine creating a state religion of the Roman Empire didn't help matters.
The Industrial Revolution pretty much guaranteed change would be too rapid to be well considered and executed, and populations would grow ungovernable.
Woodrow Wilson is a really good answer, he was weak and had no conception of the forces shaping his time, to be expected really of a Calvinist minister. He had no business being in a position of real authority at such a critical moment in history.
JFK's assassination was a bigger blow than most realize, not so much because he was so great but because the Kennedy/Goldwater debates never happened and the issues of the day never really got settled. We've been stuck in 1964 politically and socially speaking longer than most of us have been alive.