Hamas has always aspired to peace and unity with Fatah. It was the Fatah(backed by Americans, Israelis and egyptians) which fell apart after unity govt was formed under the pressure of Saudi Arabia. The clear majority win of Hamas in 2006 elections was not recongnised by Americans. And non-recognition of Hamas as a major player in conflict is the problem towards the resolution of the conflict. Unity is not possible among the two factions in forseeable future. As Fatah is considered a moderate group which can come on the table, while Hamas is thought to be an extremist and non-compromising group(supported by Iran and Syria).
The proxy wars will go on........................

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Whatever mind can conceive,it can achieve - W.Clement Stone