I did have a little look at one of the sites giving dates and checked out one of the claims. Since the claim was based in the Bible it certainly should have checked out.
The site I looked at was:
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(3) The First Temple, Solomon's Temple, was destroyed in 586-587 B.C. on the ninth of Av. The Babylonians fought their way into the Temple on Av 7, and ate and caroused there until Av 9, and at evening, set the Temple on fire. It burned all night and through the next day, Av 10. See Jeremiah 52:12-13.
What Jeremiah 52:12-13 says is
12 Now on the tenth day of the fifth month, which was the nineteenth year of King Nebuchadnezzar, king of Babylon, Nebuzaradan the captain of the bodyguard, who was in the service of the king of Babylon, came to Jerusalem.
13 He burned the house of the LORD, the king's house and all the houses of Jerusalem; even every large house he burned with fire.
So all it says is that the man responsible for the burning ARRIVED on the 10th of Av. No fight, no carousing and the burning could not have started until the 10th of Av at the earliest.
You would think that the writer would actually check what the Bible says. Or did he just assume that nobody else would check ?
And there are other dates that could be taken as significant.
The Babylonian army arrives on the tenth day of the tenth month (52:4)
The people run out of food on the nineth day of the fourth month, leading to the fall of Jerusalem. (52:6-7)
Some time after that Zedekiah is caught, his sons killed before his eyes, he is blinded and sent to Babylon (52:9-11)
I have now checked the following claim:
9) In 1914, on Av 9, World War I was declared, as Russia mobilized for war and launched bitter persecutions against Jews in Russia, which led many Jews to emigrate to the Holy Land to escape.
Germany's Declaration of War on Russia was the day before - the 8th - August 1 1914. Russia's mobilisation was earlier - July 29. But of course for the start of WW I there is the Assassination of the Archduke (June 28), Austria-Hungary's Declaration of War on Serbia (July 28) and Austria-Hungary was at war with Russia by August 6.
(
http://collections.ic.gc.ca/turner/tline1.html)
So they are wrong on two easily checked claims.