My go to for this is question is the `Tuskegee Study of Untreated Syphilis in the Negro Male` (aka. Tuskegee Experiments). Where government clinicians withheld the diagnose and treatment of syphilis from the 'participants'. The men were instead told they had 'bad blood'. This lasted into the 1970s. Only ending due to an upstanding epidemiologist, Peter Buxtun, going to the press.

https://en.wikipedia.org/wiki/Tuskegee_syphilis_experiment

https://en.wikipedia.org/wiki/Peter_Buxtun

"Buying" human experimentation data from Japan in exchange for amnesty for prosecution of war crimes (Patton).

https://en.wikipedia.org/wiki/Unit_731

https://warpardons.wordpress.com/unit-731/

• The CIA's experiments on American and Canadian citizens [0][1].

• Plans to nuke the Moon [2].

are the ones I can think of off the top of my head. Not sure if they count as "that most of us don't know about."

[0] https://en.wikipedia.org/wiki/Project_MKUltra

[1] https://en.wikipedia.org/wiki/Unethical_human_experimentatio...

[2] https://en.wikipedia.org/wiki/Project_A119

maybe this https://en.wikipedia.org/wiki/Tulsa_race_riot where a large, fairly wealthy neighbourhood of black people was firebombed by the local militia.

MKULTRA? Difficult to guess how many americans/Chinese know about a topic, however.

Being the first nation on the globe to bring in eugenics based compulsory sterilisation laws, which influenced Nazi ideas. Some survived surprisingly long after the war, the last until the 1970s.

The Rockefeller Foundation helped develop and fund various German eugenics programs.

https://en.wikipedia.org/wiki/Eugenics_in_the_United_States

Firebombing of Japan

Bombing the shit out of Laos

Massive numbers killed in the CIA operations overthrowing governments in South America

The duplicitous and two-faced foreign policies which fund genocides and killings all over the globe while we try to put on some good face about making the world a better more democratic place

Selling arms to murderous regimes who torture and kill as we turn a blind eye to profits

Repatriating Nazis responsible for the war crimes we decry in order to get their tech/medical advancements

The extent at which Native Americans were murdered

Lots and lots of things get rose-colored glasses because the populous lives rather comfortable now...