"A lot of different factors"... it's true that they're not that many but it isn't: 'we hate the jews, and everyone will die for the cause!' . I'll come back to that point after a bit of a history lesson.
About the Lebanese war:
At its root, Lebanon's war(and its ongoing troubles) is an identity crisis. Lebanon, initially, used to be just Mount Lebanon, a predominantly Maronite Christian governorate under ottoman rule. Most of the coastal areas, as well as the Bekaa valley were part of Syria(or Syria in it form then) and were predominantly Sunni Muslim. When the French and British divided the spoils of the first world war, Lebanon was placed under French mandate and enlarged to "Greater Lebanon" or Lebanon in its modern form. What you got was a country with two very different populations with very different outlooks on the world living in one country. The Christians wanted Lebanon to be a western-looking country, the Muslims, an Arab one. The difference was so clear that in 1943 when the country achieved independence the foundation of the resulting democracy was the National Pact which basically stated that the Maronites were not to seek foreign(western) support and the Sunnis should give up their demands of uniting Lebanon to Syria.
This all might actually have worked, if the inherent tensions in such cohabitation of two radically different communities wasn't stressed to such a great extent and so repeatedly by the creation of the state of Israel in the south and all the problems that this caused.
Iran, the muslim brotherhood, and all that other stuff was a much more recent development in Lebanon, mostly a byproduct of the war than anything else. It's funny how you pin the blame on Iran for example, when its foothold in Lebanon's south through Hizbullah was born out of the 1982 invasion of Lebanon by non other than Israel. The Shiite population of the south, which until then had been simple farmers and mostly absent from local politics decided to resist the invader. And out of the chaos that ensued, Hizbullah was born through Iranian intervention.
'we hate the jews, and everyone will die for the cause!' . Arabs don't(or at least didn't use to) hate jews. Now get that through your thick skull. Israel's constant whining as an oppressed state, surrounded by enemies is sickening. Like a bully after having beaten up all the other kids whines about how nobody likes him.
In the early 1900s there was barely any jewish population anywhere in the middle east. Definitely less than 10%. When jews from all over the world decide to migrate 'en masse' to a certain region of the world, then forcefully push out the initial occupants you can be sure that those occupants are going to hate them. It's quite natural, it's human. When millions of Palestinans, to this day, live in refugee camps in sub-human conditions with nothing to do except think about how they were robbed of their lands you can be damned sure that they're going to hate the jews. It's natural.
"Global Terrorism" and "Militant Islam" as they exist in their recent form were born of Israel's actions, their repeated disregard for the humanity of anyone non-jewish and their bullying of neighbor states.