"The magic world hasn't been completely out of the trauma they experienced during the time of Voldemort. So, any dark activity that happens triggers panic attacks in wizards/witches suffering from depression."
Defense Against the Dark Arts is the class that teaches defensive magic to students so they can protect themselves against the Dark Arts. Often simply referred to as DADA class.The position of DADA professor was cursed by Tom Riddle when Dumbledore refused to let him teach at Hogwarts. Every professor only held the position for exactly one year, and their tenure ended in some drastic untimely way.
"A wizard is never late, nor is he early. He arrives precisely when he means to.", says Lightning McQueen, when asked if he could have done this sooner.