Can anyone point me to a religiously-based discussion of why so many bad things happened to us Jews on Tish'a b'Av in particular, far more than on any other day on the calendar? In some cases the "bad guys" could have planned it that way, to rub it in, but in others they probably didn't. What is the teaching here?
From the Medrash Rabbah (16:20) on Bamidbar 14:1, when the people cried following the report of the Spies:
שֶׁבָּכוּ בְּלֵיל תִּשְׁעָה בְּאָב, וְאָמַר לָהֶם הַקָּדוֹשׁ בָּרוּךְ הוּא אַתֶּם בְּכִיתֶם בְּכִיָּה שֶׁל חִנָּם לְפָנַי, אֲנִי אֶקְבַּע לָכֶם בְּכִיָּה לְדוֹרוֹת, וּמִן אוֹתָהּ שָׁעָה נִגְזְרָה עַל בֵּית הַמִּקְדָּשׁ שֶׁתִּתְחָרֵב, כְּדֵי שֶׁיִּגְלוּ יִשְׂרָאֵל לְבֵין הָאֻמּוֹת, שֶׁכֵּן הוּא אוֹמֵר (תהלים קו, כו כז): וַיִּשָֹּׂא יָדוֹ לָהֶם לְהַפִּיל אוֹתָם בַּמִּדְבָּר, וּלְהַפִּיל זַרְעָם בַּגּוֹיִם וּלְזָרוֹתָם בָּאֲרָצוֹת, נְשִׂיאוּת יַד כְּנֶגֶד נְשִׂיאוּת קוֹל.
Because the congregation wept in the night of the Ninth of Ab, the Holy One, blessed be He, has said, “You have wept for nothing in front of Me. I shall establish this night for you as [a night of] a weeping for [future] generations.” And from that hour a decree on the Temple was ordained for it to be destroyed and that the Children of Israel would go in exile among the nations. It is so stated (in Ps. 106:26-27), “So He raised His hand toward them [in an oath], to make them fall in the wilderness. And to make their seed fall among the gentiles, even to scatter them among the lands.” The raising of [the divine] hand was corresponding to the lifting up of the voice (in Numb. 14:1).