They having a blast over there

We traded gold, diamonds, and land for bibles

Tough question. The island of Saint Bartholomew functioned as a dealer in the Atlantic slave trade but during WWII we sent Jewish refugees back to Germany with a big "juden" stamped in their passports.

Holy shit, so I googled it and ammonium nitrate is the most plausible explanation for the Beirut explosion.

Pioneered race biology?
Saying we were neutral in WW2 while supporting both the Nazi and the Allies?

Rounding up all the Tasmanian aboriginal people and pushing them off a cliff.

Apartheid... Or ending it, depending on your views