But today's fast, the Tenth of Tevet, is different. It was originally established to mark the beginning of the siege of Jerusalem which led to the destruction of the First Temple in the year 588 BCE, but since the founding of the State of Israel it has acquired new meaning that makes it so much more poignant.
The following question has always troubled me: How is it possible that we don't have a fast day to commemorate the Holocaust?! We're supposed to fast for a Gedaliah who lived thousands of years ago, or for the destruction of the Temple for which we feel no personal connection -- but we don't have a fast to commemorate the systematic murder of 6 million of our fathers and mothers and brothers and sisters that happened half a century ago?!
It was precisely this dissonance that caused the Rabbinate of Israel to add new meaning to this day by turning the Fast of the Tenth of Tevet into a religious memorial day for the Holocaust victims. On the Tenth of Tevet of 1949, Chief Rabbi Untermann declared that
the day on which the first hurban (destruction) commenced should become a memorial day also for the last hurban.
Two years later, the Israeli Rabbinate decided officially to turn this fast day into a memorial day for Holocaust victims, and recommended that we say kaddish for the victims whose date of death or place of death is unknown. Hence, this Fast Day has become known as Yom Hakaddish HaKlali, the General Kaddish Day.
If you can't fast, at least light a Ner Zikaron to memorialize this tragedy of epic proportions, this incomprehensible horror which is still seared into our collective memory.