There were five events that happened to our ancestors on the seventeenth of Tammuz and five on the ninth of Av. On the seventeenth of Tammuz: The tablets were shattered; The tamid (daily) offering stopped; The [walls] of the city were breached; And Apostomos burned the Torah, and placed an idol in the Temple.
On the ninth of Av, it was decreed that our ancestors should not enter the land; the Temple was destroyed the first and the second time; [the town of] Beitar was captured; and the city was plowed up.
When Av enters, they [the Jews] limit their rejoicing.
Tisha B'Av in Modern History
https://en.wikipedia.org/wiki/Tisha_B%27Av
Over time, Tisha B'Av has come to be a Jewish day of mourning, not only for these events, but also for later tragedies which occurred on or near the 9th of Av. References to some of these events appear in liturgy composed for Tisha B'Av (see below).
- The First Crusade officially commenced on August 15, 1096 (Av 24, AM 4856), killing 10,000 Jews in its first month and destroying Jewish communities in France and the Rhineland.
- The Jews were expelled from England on July 18, 1290 (Av 9, AM 5050).
- The Jews were expelled from France on July 22, 1306 (Av 10, AM 5066).
- The Jews were expelled from Spain on July 31, 1492 (Av 7, AM 5252).
- Germany entered World War I on August 1–2, 1914 (Av 9–10, AM 5674), which caused massive upheaval in European Jewry and whose aftermath led to the Holocaust.
- On August 2, 1941 (Av 9, AM 5701), SS commander Heinrich Himmler formally received approval from the Nazi Party for "The Final Solution." As a result, the Holocaust began during which almost one third of the world's Jewish population perished.
- On July 23, 1942 (Av 9, AM 5702), began the mass deportation of Jews from the Warsaw Ghetto, en route to Treblinka.
- The AMIA bombing, of the Jewish community center in Buenos Aires, killed 85 and injured 300 on July 18, 1994 (10 Av, AM 5754).
מקדש ראשון מפני מה חרב? מפני ג' דברים שהיו בו ע"ז וגלוי עריות ושפיכות דמים...אבל מקדש שני שהיו עוסקין בתורה ובמצות וגמילות חסדים מפני מה חרב? מפני שהיתה בו שנאת חנם ללמדך ששקולה שנאת חנם כנגד שלש עבירות ע"ז גלוי עריות ושפיכות דמים.
Why was the First Temple destroyed? For three things: idol worship, sexual immorality and bloodshed....
However, considering that the people during the Second Temple period were engaged in Torah study, observance of mitzvot, and acts of kindness, and that they did not perform the sinful acts that were performed in the First Temple, why was the Second Temple destroyed? For baseless hatred [sinat chinam], to teach you that baseless hatred is equal in weight to the three sins of idol worship, sexual immorality and bloodshed.
אקמצא ובר קמצא חרוב ירושלים,דההוא גברא דרחמיה קמצא ובעל דבביה בר קמצא עבד סעודתא אמר ליה לשמעיה,זיל אייתי לי קמצא אזל אייתי ליה בר קמצא,אתא אשכחיה דהוה יתיב אמר ליה,מכדי ההוא גברא בעל דבבא דההוא גברא הוא מאי בעית הכא,קום פוק,אמר ליה,הואיל ואתאי שבקן ויהיבנא לך דמי מה דאכילנא ושתינא אמר ליה,לא,אמר ליה,יהיבנא לך דמי פלגא דסעודתיך,אמר ליה,לא,אמר ליה,יהיבנא לך דמי כולה סעודתיך,א"ל,לא,נקטיה בידיה ואוקמיה ואפקיה,אמר,הואיל והוו יתבי רבנן ולא מחו ביה ש"מ קא ניחא להו איזיל איכול בהו קורצא בי מלכא,אזל אמר ליה לקיסר,מרדו בך יהודאי,א"ל,מי יימר,א"ל,שדר להו קורבנא חזית אי מקרבין ליה,אזל שדר בידיה עגלא תלתא,בהדי דקאתי שדא ביה מומא בניב שפתים ואמרי לה בדוקין שבעין דוכתא דלדידן הוה מומא ולדידהו לאו מומא הוא,סבור רבנן לקרוביה משום שלום מלכות אמר להו רבי זכריה בן אבקולס יאמרו,בעלי מומין קריבין לגבי מזבח,סבור למיקטליה דלא ליזיל ולימא אמר להו רבי זכריה יאמרו,מטיל מום בקדשים יהרג,אמר רבי יוחנן,ענוותנותו של רבי זכריה בן אבקולס החריבה את ביתנו ושרפה את היכלנו והגליתנו מארצנו
Yerushalayim was destroyed due to [the incident involving] Kamtza and Bar Kamtza. There was a man who was a close friend of Kamtza and an enemy of Bar Kamtza. He made a party and told his servant to invite Kamtza. The servant brought him Bar Kamzta. The host found Bar Kamtza sitting. The host said to him: "Since you are my enemy, what are you doing here? Get up and leave!"
Bar Kamtza said to him: "Once I have come, leave me be and I will pay for everything I eat and drink."
"No!"
"I will pay for half the party."
"No!"
"I will pay for the entire party."
"No!" He took him by the hands, picked him up and threw him out.
Bar Kamtza said: "Since the rabbis were sitting there and did not protest, it seems that they were pleased with what happened. I will go and slander them before the emperor."
He said to the Caesar: "The Jews are rebelling against you."
"How do you know this?"
"Send them a sacrifice and see if they offer it."
The Caesar went ahead and sent with him a healthy calf. While he was on the way, he placed a blemish on the animal's upper lip; some say he caused a cataract on the eye. These things are blemishes for us (and disqualify an animal for sacrificing) but not for them (the Romans).
The Rabbis wanted to offer it (despite its disqualifying blemish) to preserve good relations with the authorities.
R. Zekharya ben Avkolus said to them: "People will then think that blemished animals may be offered upon the altar."
They wanted to kill the person who brought the animal, so he could not go and inform on them. R. Zekharya ben Avkolus said: "People will say that anyone who places a blemish in a sacrifice should be killed."
R. Yochanan said: "The humility of R. Zekharya ben Avkolus destroyed our temple, burned our sanctuary and exiled us from our land."
Orot HaKodesh
Rabbi Abraham Isaac Kook (1865 - 1935)
First Ashkenazi Chief Rabbi of Palestine under the British Mandate
“If we were destroyed, and the world with us, due to sinat chinam, baseless hatred, then we shall rebuild ourselves, and the world with us, with ahavat chinam, baseless love.”