Comment by yoavm
First, I forgot an 's there - I meant 1970s. Second, unfortunately for Lebanon, Hezbollah wasn't the only terrorist organization growing in it [0]. "The proximate cause of the Israeli invasion was the Coastal Road massacre that took place near Tel Aviv on 11 March 1978"
[0] https://en.wikipedia.org/wiki/1978_South_Lebanon_conflict
Hezbollah was founded in 1982. With benefit of hindsight we can see that while Israel's Lebanon Invasion in 1980s was successful in curbing the PLO who perpetrated the massacre, they created a more formidable adversary in form of Hezbollah.