To take a particularly bad one that relatively frequently comes up, consider the Congo Free State [1], which is considered bad enough by some still that a statue showing king Leopold II being celebrated by the Congolese was vandalised by someone chopping off the hand of one of the African characters to symbolise the history of chopping off the hands of those who refused to work the rubber plantations.

But the list is massive.

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

Colonizations, almost all of my friends from international communities had their countries colonized by Western powers. A lot of them still blame colonization for current problems in their countries.