Well, they had lockdowns in 1918 too until the flu died down. The problem is not the lockdown but the duration of it.
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I've seen people make this claim, but I haven't seen any evidence for it. All I've seen is that theaters, churches, bars, dance halls, and other places of public gathering were closed during Spanish Flu. I have yet to see any evidence that:
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Stores were closed.
Offices and factories were closed.
Restaurants were closed except for take-out.
People were ordered to stay within their homes except to go to the grocery store or a couple of other exceptions.
People were told they could not go to the house of a family member or friend except to provide urgently-needed medical care.
People could not invite anyone over to their house.
People were ordered not to take exercise even out of doors except within their immediate neighborhood.
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However, this past year ALL of these things were mandated in most states of this country. Indeed, for several months, most of the human race was living under substantially the same rules as what I provided, something without precedent in 6,000 years of human history, and that no one could ever imagine was even possible.