The 1982-85 Lebanon War can also be treated as the third phase of the 1975-90 Lebanese Civil War, following its first (the Lebanese National Movement and the PLO against the Christian Phalanges) and second (the Phalanges against the intervening Syrian army and the PLO against Israel) phases. But as it does involve a discrete event—the invasion of Lebanon by the Israeli army—it’s also perfectly reasonable to treat it this conflict as a discrete-albeit-related affair, and anyway this is my website so I can do what I want.
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The Foreign Exchanges Companion 
Excellent summary and analysis. June-September of 1982 was indeed the worst period of the war. In fact, most of those 20,000+ dead Lebanese and Palestinians were killed in those 4 months alone.