
Which was mostly done by the British, French, Spanish, Dutch, and Russians (Alaska) before the US became a country. Yes, the genocide of the Native Americans was an atrocity, but 90% of it happened within 100 years after Columbus arrived. Even so there was no 5 year period in the US to be that came close to as many deaths as the the years of the Russian Civil War.
Looks like I misremembered. It was popularized following the assassination of Tsar Alexander II.
https://encyclopedia.ushmm.org/content/en/article/pogroms
There were a LOT of pogroms during the Russian Civil War, like 1,500 just from 1918-1920.
https://en.m.wikipedia.org/wiki/Pogroms_during_the_Russian_Civil_War