What was Black September? It was what the PLO called the period were JORDAN killed thousands of Palestinians (fighter and civilians), when Jordan decide to drive the PLO out in 1970.
So, the PLO gets revenge for a massacre by Jordan is kill Israelis.
Interesting, Indeed.
http://www.palestinefacts.org/pf_1967to1991_jordan_expel_plo.php
Feud everlasting.