Religion examples. In 1833 William Miller predicted the return of Jesus Christ in 1943 and people took specific actions.
How many people?
I couldn’t find the answer on the Wikipedia page, but it sounds like it was a big deal. One data point is this (from the Wikipedia page):
As the various dates of Christ’s predicted return approached, Millerite publishing went into high gear. In May 1843, 21,000 copies of the various Millerite papers were published for distribution each week. In New York alone, in the five-month period ending April 1843, 600,000 copies of various publications were distributed. In December 1843, Himes proposed the publication of one million tracts, while in May 1844, he announced that five million copies of Millerite publications had been distributed up to that time.[11]
Another is that Miller spawned the Seventh-Day Adventists who have approximately 17M members today.
Eugenics people
Did they have any impact? Could they plausibly have?
They certainly thought they could have a big impact. There was no precedent of them having the impact they wanted. And it was a major movement. I have no sense of how feasible their strategies should have looked at the time.
I couldn’t find the answer on the Wikipedia page, but it sounds like it was a big deal. One data point is this (from the Wikipedia page):
Another is that Miller spawned the Seventh-Day Adventists who have approximately 17M members today.
They certainly thought they could have a big impact. There was no precedent of them having the impact they wanted. And it was a major movement. I have no sense of how feasible their strategies should have looked at the time.