Everyone talks about how Sinas Chinam destroyed the Beis Hamikdash. Given the amount of Machlokes, Lashon Hara etc. we have among us today - there is nothing more fitting to talk about.
But I would like to remind everyone that it was on Tisha B'av that the Meraglim came back with a bad report about ERETZ YISROEL and the Jews cried, not accepting the words of Yehoshua and Calev that "טובה הארץ מאד מאד". B/c the Jews rejected Eretz Yisroel - they all died in the desert. Had they not done so they would have marched straight into EY, built the Beis Hamikdash and the last few thousand years would have been bliss instead of the nightmare it has been.
I don't want to say too much but the message of the bad Meraglim is echoed all too often even in our day and the number of people who have no interest in living in Hashem's Land is too large. ודי לחכמיא.
Tisha B'av is a GREAT time to make the tikkun!!!
Note: There is NO opinion [of which I am aware] that holds that in our days Eretz Yisroel is a land like all other lands. Regardless of whether שמיטה and תרומות ומעשרות are מדאורייתא or מדרבנן, Eretz Yisroel remains THE Holy Land and the subject of our special covenant with Hashem.
To reject Hashem's gift is simply insulting. So if one can't practically live here - the hope and aspiration MUST be to come. This is not "Zionism". This is Judaism. This is Torah.