Answer: A lot of things happened on the Ninth of the Hebrew month of Av. Here are seven:
1) The book of Numbers recounts that the Israelite spies returned from spying out the Land of Canaan (which later became the land of Israel) and gave a report on what they saw which made the Land sound like a bad place. As a result, the Children of Israel cried for no valid reason, so death was decreed upon the entire generation before their children entered the Land.
2) and 3) Both the First and Second Temples in Jerusalem were destroyed; the first by Nebuchadnezzar's Babylonian Army in 423 BCE, and the second by Titus's Roman Army in 68 CE.
4) The Romans massacred the inhabitants of the Judean town of Betar after Bar Kochba's rebellion failed following the destruction of the Second Temple.
5) The Roman commander, Turnus Rufus, plowed over the site of the Temple Mount in Jerusalem.
6) The Jews were expelled from Spain at the start of the Spanish Inquisition in 1492.
7) World War I began, which started off a chain of events leading to the Holocaust.
See https://www.hebcal.com/hebcal/?year=1492;v=1;month=x;yt=G;nh=on;nx=on;i=off;vis=0;D=on;d=on;c=off;geo=zip#cal-1492-07, the ninth of Av in 1492 was August 11, 1492. The Expulsion of the Jews was effective July 31, 1492. Close, but no cigar.
Start of WWI: Tue, 28 July 1914 = 5th of Av, 5674. See https://www.hebcal.com/converter/?gd=28&gm=7&gy=1914&g2h=1
My favourite poet, Natan Alterman, was born~
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