The primary cause of the attack by Black September would be the Israel-Palestinian conflict.
In the late 1960s, Palestine had attacked Israel on numerous occasions via Jordan, triggering a reaction from Israel. Tensions grew between the two governing bodies of the two countries.
In July of 1971, the Palestine Liberation Organization was expulsed to Lebanon by Jordan.
Many Palestinians immigrated to Lebanon after Black September and a 1969 agreement allowed them autonomy within the southern part of Lebanon.
The PLO launched rockets aimed at Israeli villages within South Lebanon and bu the early 1970s, Palestinian terror organisations began an international campaign against the Israelis in Europe. Through various means of terrorism, such as the Munich Massacre, they aimed to publicize the Palestinian cause.
Thus, we can see that political reasons were the cause of the Massacre.
