Why do Jews FAST today?

hear the one about the wall it's hilarious I'm still trying to get over it okay I'm going to tell you one about the wall this is not a joke though actually the opposite of a joke it's very very sad very sad thing connected to a wall the 17th of tamos is one of the public fast days that were established by our sages in order to commemorate and to mourn for the incidents connected to the destruction of the B of English the Holy Temple in Jerusalem specifically what is the event connected to the s of T is that is the day of the splitting of the wall there was a city wall or protective wall around yush around the holy city of Jerusalem and on the 17th of T the wall was split we know what happened 3 weeks later on Tish of on the 9th of of that's when the temple itself was destroyed but 3 weeks prior to that on the 17th of T that is when the city walls were split and uh therefore we fast on that day as well