The Twentieth of Sivan
was
designated to commemorate a number of attacks on Jewish communities throughout Europe, beginning with a blood libel in France in 1171 that resulted in the execution of 32 innocent Jewish men and women on the 20th of
Sivan
that year.
In 1648, the Ukrainian Cossack leader Bogdan Chmielnizki incited his followers against the Jews of the Ukraine. In the pogroms that followed, hundreds of thousands of Jews were murdered, and entire communities were wiped out.
Their first attack was against the city of Nemirov on the 20th of Sivan, and over 6,000 Jewish men, women, and children were slaughtered on that day.
The Cossack "armies" then ravaged Tulshin, Polannoe, Ostrog, and Zaslow. In Uman, over 30,000 Jews were brutally tortured and killed because they refused to bow to an idol. It was with these holy martyrs that Rebbe Nachman wished to remain after his passing.
In 1650, rabbinic leaders assembled as a "Council of the Four Lands" to proclaim the 20th of Sivan—the day Nemirov was attacked—as a day of commemoration for the martyrs of the Chmelnitzki massacres.
It's no longer a widespread custom to fast on this day (some individuals fast half the day) but giving charity is appropriate. To hear more, click the link below.
