Israel's alliance with the Phalangists in Lebanon, that was largely the work of my unfavorite person, Sharon. It is not accurate to say that they entered it because the had the same opponents - the Palestinians, Amal and the Hezbollah. Hezbollah wasn't founded at the time when Israel invaded Lebanon, it was a product of the occupation. Up until 1980, Israel had a good relationship with Amal, which represented a conservative Shia view, hostile to the PLO. (The type of view which one finds in the writings of Fouard Ajami.) But they swapped that for an alliance with Gemayel's forces. The lure was ideological (it can't have been tactical - the Maronite forces were as useless as tits on a bull.) The Kataeb (Phalangists) were left overs from 1936. The Lebanese Jews could tell you a thing or two about them.
Sharon has been a diaster for Israel. As minister of housing he's the one would started diverting money to build all the settlements in the occupied territories. He said he did it to establish "facts on the ground," meaning it would much harder for any future prime minister to ever consider giving back the land if settlers had build their homes there. He was right too. What he didn't forsee was that the formerly compliant and docile Palestinians, who in some cases welcomed the IDF with cups of coffee and cries of shalom in the 1967 war, would eventually turn against the checkpoints and permits and quotas and Israeli-only highways. Now, I really don't think there's any solution to the problem (at least not a humane one). The Palestinians are so furious and bereft of hope they are willing to blow themselves up in order to kill Israelis. The Israelis say, quite correctly, you can't just expect us not to defend ourselfs while suicide bombers blow up our children. Both sides see their (self-defeating) actions as completly justified. So the Palestinian bombings go on and the Israeli attacks on Palestinian cities go on. And the person who put both sides in this incredible mess from which there is no exit is Ariel Sharon.