Everyone in New Orleans was playing jazz on March 19, 1919. That's because The Axeman (a guy who had been periodically entering people's houses late at night so that he could kill and maim them with an axe) had written a letter to the local newspapers, threatening that he would kill anyone who wasn't playing jazz music. The newspapers actually printed the letter.
From Wiki:
The Axeman's Letter.Hell, March 13, 1919
Esteemed Mortal of New Orleans:The Axeman
They have never caught me and they never will. They have never seen me, for I am invisible, even as the ether that surrounds your earth. I am not a human being, but a spirit and a demon from the hottest hell. I am what you Orleanians and your foolish police call the Axeman.
When I see fit, I shall come and claim other victims. I alone know whom they shall be. I shall leave no clue except my bloody axe, besmeared with blood and brains of he whom I have sent below to keep me company.
If you wish you may tell the police to be careful not to rile me. Of course, I am a reasonable spirit. I take no offense at the way they have conducted their investigations in the past. In fact, they have been so utterly stupid as to not only amuse me, but His Satanic Majesty, Francis Josef, etc. But tell them to beware. Let them not try to discover what I am, for it were better that they were never born than to incur the wrath of the Axeman. I don't think there is any need of such a warning, for I feel sure the police will always dodge me, as they have in the past. They are wise and know how to keep away from all harm.
Undoubtedly, you Orleanians think of me as a most horrible murderer, which I am, but I could be much worse if I wanted to. If I wished, I could pay a visit to your city every night. At will I could slay thousands of your best citizens (and the worst), for I am in close relationship with the Angel of Death.
Now, to be exact, at 12:15 (earthly time) on next Tuesday night, I am going to pass over New Orleans. In my infinite mercy, I am going to make a little proposition to you people. Here it is:
I am very fond of jazz music, and I swear by all the devils in the nether regions that every person shall be spared in whose home a jazz band is in full swing at the time I have just mentioned. If everyone has a jazz band going, well, then, so much the better for you people. One thing is certain and that is that some of your people who do not jazz it out on that specific Tuesday night (if there be any) will get the axe.
Well, as I am cold and crave the warmth of my native Tartarus, and it is about time I leave your earthly home, I will cease my discourse. Hoping that thou wilt publish this, that it may go well with thee, I have been, am and will be the worst spirit that ever existed either in fact or realm of fancy.
--The Axeman
Also from Wiki:
Motivated by press coverage of a mysterious letter sent to newspapers from the purported ax murderer promising those who were not playing jazz music on March 19 "will get the axe", dance halls in New Orleans were filled to capacity and hundreds of professional and amateur jazz musicians were hired to play at private parties in residential homes as a way to protect from attacks. No murders occurred that night.
Info on The Axeman:
https://en.wikipedia.org/wiki/Axeman_of_New_Orleans
