Khmelnytsky Uprising

Cossack rebellion within the Polish–Lithuanian Commonwealth in 1648–1657

Early 20th-century estimates of Jewish deaths were based on the accounts of the Jewish chroniclers of the time, and tended to be high, ranging from 100,000 to 500,000 or more;

A 2003 study by Israeli demographer Shaul Stampfer of Hebrew University dedicated solely to the issue of Jewish casualties in the uprising concludes that 18,000–20,000 Jews were killed...

...the Ukrainian-American historian Jarowlaw Pelenski narrows the number of Jewish deaths to between 6,000 and 14,000.

https://en.wikipedia.org/wiki/Khmelnytsky_Uprising?wprov=sfla1