(א) מִצְוַת עֲשֵׂה מִן הַתּוֹרָה לִזְעֹק וּלְהָרִיעַ בַּחֲצוֹצְרוֹת עַל כָּל צָרָה שֶׁתָּבוֹא עַל הַצִּבּוּר. שֶׁנֶּאֱמַר (במדבר י ט) "עַל הַצַּר הַצֹּרֵר אֶתְכֶם וַהֲרֵעֹתֶם בַּחֲצֹצְרוֹת". כְּלוֹמַר כָּל דָּבָר שֶׁיָּצֵר לָכֶם כְּגוֹן בַּצֹּרֶת וְדֶבֶר וְאַרְבֶּה וְכַיּוֹצֵא בָּהֶן זַעֲקוּ עֲלֵיהֶן וְהָרִיעוּ:
(1) 1 It is a positive commandment from the Torah to cry out and to sound trumpets for all troubles that come upon the community; as it is stated (Numbers 10:9), "upon an enemy who attacks you and you sound trumpets." That is to say, [with] every matter that troubles you - such as famine, a plague, locusts and that which is similar to them - cry out about them, and sound the trumpets.
(א) יֵשׁ שָׁם יָמִים שֶׁכָּל יִשְׂרָאֵל מִתְעַנִּים בָּהֶם מִפְּנֵי הַצָּרוֹת שֶׁאֵרְעוּ בָּהֶן כְּדֵי לְעוֹרֵר הַלְּבָבוֹת לִפְתֹּחַ דַּרְכֵי הַתְּשׁוּבָה וְיִהְיֶה זֶה זִכָּרוֹן לְמַעֲשֵׂינוּ הָרָעִים וּמַעֲשֵׂה אֲבוֹתֵינוּ שֶׁהָיָה כְּמַעֲשֵׂינוּ עַתָּה עַד שֶׁגָּרַם לָהֶם וְלָנוּ אוֹתָן הַצָּרוֹת. שֶׁבְּזִכְרוֹן דְּבָרִים אֵלּוּ נָשׁוּב לְהֵיטִיב שֶׁנֶּאֱמַר (ויקרא כו, מ) "וְהִתְוַדּוּ אֶת עֲוֹנָם וְאֶת עֲוֹן אֲבֹתָם" וְגוֹ':
(1) 1 ---
דאמר רב חנא בר ביזנא אמר ר"ש חסידא מאי דכתיב (זכריה ח, יט) כה אמר ה' צבאות צום הרביעי וצום החמישי וצום השביעי וצום העשירי יהיה לבית יהודה לששון ולשמחה קרי להו צום וקרי להו ששון ושמחה בזמן שיש שלום יהיו לששון ולשמחה אין שלום צום אמר רב פפא הכי קאמר בזמן שיש שלום יהיו לששון ולשמחה יש גזרת המלכות צום אין גזרת המלכות ואין שלום רצו מתענין רצו אין מתענין אי
As Rav Ḥana bar Bizna said that Rabbi Shimon Ḥasida said: What is the meaning of that which is written: “Thus said the Lord of hosts: The fast of the fourth month, and the fast of the fifth, and fast of the seventh, and the fast of the tenth, shall become times of joy and gladness, and cheerful seasons, to the house of Judah” (Zechariah 8:19). It calls them days of “fast” and it calls them “times of joy and gladness.” How so? When there is peace in the world, they will be times of joy and gladness, on which eulogies and fasting are forbidden; but when there is no peace, they are days of fasting. In a time when there is no peace, why are messengers not sent out also for the fourth and tenth months, so that people can know when to observe the fasts? Rav Pappa said that this is what it is saying: When there is peace in the world and the Temple is standing, these days will be times of joy and gladness; when there is persecution and troubles for the Jewish people, they are days of fasting; and when there is no persecution but still no peace, neither particular troubles nor consolation for Israel, the halakha is as follows: If people wish, they fast, and if they wish, they do not fast. Since there is no absolute obligation to fast, messengers are not sent out for these months.
Summary of the Rivta on Rosh Hashanah 18b
Questions the Gemara: How can fast days that commemorate the Destruction of the Beit Hamikdash be canceled before the construction of a Beit Hamkidash?
Suggests a different understanding of the Gemara: During time of peace without the Beit Hamikdash, the Jewish people can determine the stringencies of the fast. It's up to them to decide wether they want to refrain from bathing, leather shoes, anointing, and sex.
Adds that now because communities never took these stringencies upon themselves, we don't uphold them.
The Rivta's understanding of the Gemara is a minority opinion among the rest of the Rishonim. Most Rishonim understand the Gemara as during a time period of shalom and no gezeriat malchut, communities may decide wether or not to observe these fasts...
So how do we define shalom and gezeriat malchut? Do we need both? How does autonomy of Israel fit into the question?
דאמר רב חמא בר ביזנא כו' - דכולהו ימי תענית נינהו בזמן הזה שאין בהמ"ק קיים ומתניתין בזמן הזה קא מיירי מדקתני וכשהמקדש קיים כו': שיש שלום - שאין יד העובדי כוכבים תקיפה על ישראל: יהיו לששון ולשמחה - ליאסר בהספד ובתענית:
We fast when we do not have the Beit Hamikdash, and we don't have to fast when we have the Beit Hamikdash.
Shalom is when the Jewish people have dominion over Israel.
It's unclear wether or not Rashi maintains that having shalom is enough to abolish a fast day. It seems that he thought when we have domion over Israel, we would also have the Beit Hamikdash...
...
Peninei Halacha
How does Gezeirat Malchut fit into this discussion?
"However, some [authorities] maintain that Jews must observe full-day fasts in every generation during periods of [anti-Jewish] decrees and religious persecution. This seems to be the simple understanding of the Talmudic discourse as explained by the Ramban and the other poskim. That is, whenever there are [harsh] decrees, the obligation to fast returns to its original status and the three fasts take on the laws of Tish’a B’Av. The Tashbetz (2:271) concurs, but he writes that if the persecutions affect part of the Jewish people, only they need to fast an entire day. It is possible, though, that even they are [exempt from this stringency, seeing that they are considered] “under duress” because of the persecutions."
והא דלא נפקי אתמוז ואטבת מפני התענית משום דאמרי' ע"ב יש צרה צום אין צרה ואין שלום רצו מתענין רצו אין מתענין פי' לא רצו הציבור. אבל היחיד אין לפרוש מן הציבור כל זמן שלא נמנעו הציבור שלא להתענות:
Question: During a time period where there is no gezeriat malchut and no shalom, do we still have to fast?
Responce: It's up to communities to decide and an individual must stick to the practice of his community.
(א) על ששה חדשים השלוחין יוצאין כו': ובבית שני לא היו מתענין לא עשרה בטבת ולא שבעה עשר בתמוז אלא מי שהיה רוצה מתענה ומי שלא היה רוצה לא היה מתענה .
During the time period of the Second Beit Hamikdash, people who wanted to fast, fasted and those who didn't want to didn't fast.
The Second Beit Hamikdash was a time when we had the Beit Hamikdash, while we were still at points under Gezairat Malchut. The Rambam seems to hold that at times when we have shalom, but are under Gezairat Malchut fast days become optional.
(יט) כָּל הַצּוֹמוֹת הָאֵלּוּ עֲתִידִים לִבָּטֵל לִימוֹת הַמָּשִׁיחַ. וְלֹא עוֹד אֶלָּא שֶׁהֵם עֲתִידִים לִהְיוֹת יוֹם טוֹב וִימֵי שָׂשׂוֹן וְשִׂמְחָה שֶׁנֶּאֱמַר (זכריה ח יט) "כֹּה אָמַר ה' צְבָאוֹת צוֹם הָרְבִיעִי וְצוֹם הַחֲמִישִׁי וְצוֹם הַשְּׁבִיעִי וְצוֹם הָעֲשִׂירִי יִהְיֶה לְבֵית יְהוּדָה לְשָׂשׂוֹן וּלְשִׂמְחָה וּלְמֹעֲדִים טוֹבִים וְהָאֱמֶת וְהַשָּׁלוֹם אֱהָבוּ":
After detailed analysis of the many halachot of fast days, the Rambam states that all these fast days will be nullified in the days of Mashiach and turn into days of joy.
Because the Rambam states that these fasts days will be nullified at the time of Mashiach, he implies that until Mashiach comes all these fast days are mandatory.
Looking at both Rambam, he seemed to hold that the conditions of Gzeirat Malchut and Shalom applied to the time periods before Chorban Beit Sheni. After the Second Beit Hamkidash is destroyed, fast days no longer become optional regardless of Gzeirat Malchut.
Why do you think the Rambam holds this opinion?
(א) הכל חייבים להתענות ארבע צומות הללו ואסור לפרוץ גדר
(1)
All are obligated to fast on these Four fasts, and it is forbidden to break the fence (i.e. not fast)
Rav Brofsky notes that Rav Yosef Cairo rules this way because the Jewish people have taken it upon themselves to accept these fasts.
...
We have seen many sources regarding the status of fast days... It is clear that during the times of the early Rishonim, the status of fast days was not so clear.
How can we understand that these fast days were left to the will of people? What is the significance that the Jewish people have took it upon themselves to continue these fast days?
(א) וַיְהִי֩ בִשְׁנַ֨ת הַתְּשִׁיעִ֜ית לְמָלְכ֗וֹ בַּחֹ֣דֶשׁ הָעֲשִׂירִי֮ בֶּעָשׂ֣וֹר לַחֹדֶשׁ֒ בָּ֠א נְבֻכַדְנֶאצַּ֨ר מֶֽלֶךְ־בָּבֶ֜ל ה֧וּא וְכָל־חֵיל֛וֹ עַל־יְרוּשָׁלִַ֖ם וַיִּ֣חַן עָלֶ֑יהָ וַיִּבְנ֥וּ עָלֶ֖יהָ דָּיֵ֥ק סָבִֽיב.
(1) And in the ninth year of his reign, on the tenth day of the tenth month, Nebuchadnezzar moved against Jerusalem with his whole army. He besieged it; and they built towers against it all around.
(א) יֵשׁ שָׁם יָמִים שֶׁכָּל יִשְׂרָאֵל מִתְעַנִּים בָּהֶם מִפְּנֵי הַצָּרוֹת שֶׁאֵרְעוּ בָּהֶן כְּדֵי לְעוֹרֵר הַלְּבָבוֹת לִפְתֹּחַ דַּרְכֵי הַתְּשׁוּבָה וְיִהְיֶה זֶה זִכָּרוֹן לְמַעֲשֵׂינוּ הָרָעִים וּמַעֲשֵׂה אֲבוֹתֵינוּ שֶׁהָיָה כְּמַעֲשֵׂינוּ עַתָּה עַד שֶׁגָּרַם לָהֶם וְלָנוּ אוֹתָן הַצָּרוֹת. שֶׁבְּזִכְרוֹן דְּבָרִים אֵלּוּ נָשׁוּב לְהֵיטִיב שֶׁנֶּאֱמַר (ויקרא כו, מ) "וְהִתְוַדּוּ אֶת עֲוֹנָם וְאֶת עֲוֹן אֲבֹתָם" וְגוֹ':
(
(1) The essential significance of the fast of the Tenth of Tevet, as well as that of the other fast days, is not primarily the grief and mourning which they evoke. Their aim is rather to awaken the hearts towards repentance; to recall to us, both the evil deeds of our fathers, and our own evil deeds, which caused anguish to befall both them and us and thereby to cause us to return towards the good. As it is said (Vayikra 26): ‘And they shall confess their transgressions and the transgressions of their fathers.’