That's to say, without outside support for Fatah, I can't see why there should've been a unity government at all.
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Huh? We saw exactly the opposite situation. You're forgetting that a primary trigger for the conflict was that Dahlan refused to fold the PA security forces (a force that nearly everyone concerned has been arming, and we in particular have been pushing to pull off a "hard coup") into the command of a politically neutral Interior Minister.
Hamas has set up their own security force, outside of MoI jurisdiction, that set up facts on the ground.
Both sides were preparing for war. Hamas was ultimately better, which is why Dahlan asked for US and Israeli assistance in the first place.
It is not like Hamas and Fatah were all about peace and love and flowers, and then suddenly evil Israel and US came and tried to hurt their relationship.
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