Rambam Hilchos Ta’aniyos 1:2-3
This is of the paths of repentance, that when disaster strikes and they cry out on its account and sound the trumpets, all will know that they were harmed due to their evil deeds … and this will bring the removal of the trouble from them. However, if they do not cry out and sound the trumpets, but rather say, “What occurred to us is the way of the world and this disaster is mere happenstance,” this is a grossly insensitive reaction and will cause them to cling to their evil ways and the disaster will be compounded by additional disasters. This is what is written in the Torah: “And you shall act towards me with keri, and I will act towards you with the wrath of that keri.” In other words, when I bring a disaster against you so that you shall repent, if you say it is keri (happenstance), I will add the wrath of that keri.
We know the churban was because of sinas chinam and pritzus (per the Gemora), Tach V’tat occurred because of talking in shul (per the Tosfos Yom Tov), the holocaust occurred because of zionism and secularism, etcetera. Our contemporary Talmidei Chachomim, just as with Tach V’tat and the holocaust, are uniquely qualified to tell us what a disaster represents.