In September 1868, Southern white Democrats hunted down around 200 African-Americans in an effort to suppress voter turnout
September 28 is the anniversary of The Opelousas Massacre in 1868. Like most massacres in the US, the violence was caused mostly by racism, but also the desire to suppress their political opponents.
In the summer of 1868, black people in Louisiana had used their newly won power to vote by voting for anti-slavery politicians. In response, the white men began forming vigilante groups that would roam the countryside and harass or lynch black people. The newspapers openly warned people to not vote for Republican candidates.
One newspaper reporter (Emerson Bentley) dared to write the truth about what had been happening in Louisiana. That was enough to kick off a whole new wave of murder. Bentley was beaten and left for dead. The other reporter at his newspaper was lynched and had is body put on display. Anyone with black skin faced summary execution. The newspapers gloated.
In the end, over 200 people lay dead at the hands of the white Americans. Most of them black, some of them sympathisers. Not a single vote was registered for the Republican party, as it had been made clear that doing so would incur the death penalty. No hearings or trials were ever held. American democracy was working as intended. Voter suppression continues to this day in Louisiana.
The Balangiga Massacre in 1901, where Imperial US troops were hit by Philippine partisans in defence of their country. The US was horrified by the loss of their jackboots and responded by issuing an order to "Kill Everyone Over Ten".
The Second Occupation of Cuba in 1906, where the US once again invaded Cuba. The US regime stayed for 3 years until they could set up a government that they liked.