The Fast Of Chof Sivan

לז"נ הקדושים מלכה בת ר' מאיר שלמה ושני בניה

 הבחור ניסן והבחור פנחס בני ר' משה הי"ד      

יום השנה הוקבעה לכ' סיון                   

כ' סיון                      

In the year 1171, 31 Yidden were burned in the city of Blois France.

1) R.Tam was Gozer Ta'anis on כ' סיון 

. He

 said

​ ​

"

this Ta'anis is greater than Tzom Gedalya being it is like Yom Kippur.

"

2) After the גזרת ת"ח ות"ט  (Chmelnitski ym"s 1648-9) The Va'ad 

Arba Artzos reintroduced the Ta'anis of 

סיון

 'כ

The מגןאברהם ס' תקפ ס"ק ה writes נוהגין להתענות כ' סיון בכל מלכות פולין

3) In 1946, The Gedolim in Hungary chose כ' סיון as a fast day to commemorate the Holocaust of six million who were murdered  by the Germans ימ"ש.  A special Selichos for כ' סיון was printed in Budapest.

In Eretz Yisroel Harav Chizkiyahu Mishkovsky zt"l along with other Gedolim tried during the war

when 

the horrible  information 

became public,  

to 

establish  a whole week of 

Aveilus (Shiva) 

and also a one

day of

Taanis. 

The Chazon Ish and Brisker Rov both opposed the idea. They held, in our generation, we are not big enough to declare

a new fast day for Klal Yisroel. 

As a result the Hungarian initiative gradually fell apart.  

R. M. Feinstein zt"l (Igros Moshe Y.D.4:57) explains that the Gezeiras Hitler ym"s was about to destroy the whole Jewish nation in the whole world.

This

 Gezeira

​ ​

is part of the original 

Gezeira

s Galus   which 

Chazal had already established the fast days. We 

are not big enough

 to add more to Takonas Chazal.

Whereas the Gezeiras תתנ"א  & ת"ח ות"ט etc. were local 

Gezeiros. In such cases, we may  be 

Gozer Ta'anis. 

The same way if an individual goes through ח"ו a צרה ל"ע may fast so too can a Kehila establish a fast.