I'm currently reading Black Hawk Down by Mark Bowden and from what I've been reading and from what I watched in the movie, the whole raid was a complete disaster as soon as the rangers rappelled from the Blackhawks. Why was it such a disaster?
Could you please clarify whether you're asking from a political POV, military POV, or something else? The mission was successful in terms of capturing the targets (a few of Aidid's lieutenants), but it had far-reaching consequences on Bill Clinton's foreign policy actions in the coming years (e.g. the decision to take limited action with regards to Rwanda).
I guess your question is unclear because you're assuming it WAS a disaster. Maybe you could rephrase?
Some of the problems that led to the disaster at Mogadishu included a combination of (1) mission creep (2) a dysfunctional civilian-military relationship and (3) internal politics among Somalia policymakers.
The initial U.S. mission in Somalia, Operation Provide Relief, is fairly successful in delivering humanitarian assistance. Bush 41, despite his realist precepts, seemed to have a humanitarian impulse: after months of stonewalling in State and among the military, he received a cable from a member of the State Department in Kenya on the conditions faced in Somalia (the United States did not maintain an active embassy in Mogadishu at the time). Now a lame duck president, he committed himself to sending U.S. troops to stop the continued famine in Somalia, whose deaths had reached a peak several months prior. Powell, who had categorically refused to take on the mission. The Bush team crafts a mission that’s limited in scope, that they initially hope will be over before Clinton’s inauguration. The troops would get in, deliver food supplies, and get out. Bush takes the opportunity to fly to Somalia to visit the troops. One of the problems is that, though the mission was designed with an exit strategy in mind, there was no political will to leave Somalia.
Enter the Clinton administration. Though Clinton had identified Somalia as a key priority for his administration during his campaign and during the transition, after becoming president, his focus is on domestic policy. He campaigned on the idea of “It’s the Economy, Stupid!” and created a mirror to the National Security Council in the National Economic Council. Most of the formulation of Clinton’s policy on Somalia is ultimately delegated to his subordinates, many of whom don’t have much experience conducting foreign policy. There had not been an NSC meeting prior to Black Hawk Down. Madeleine Albright and Bottros-Ghali represent the exceptionally pro-intervention faction, and she makes pronouncements at the United Nations about the need to engage in statebuilding in Somalia.
These problems are compounded by a constantly changing command structure (the U.N. is given control over the mission at some point prior to the defeat of Task Force Ranger.) Additionally, there is a relationship between civilian leaders and the military that is contentious at the very start. Some members of the military took issue with “don’t ask don’t tell,” (for a variety of reasons) and its sudden implementation, and there was a feeling among career bureaucrats that the Clinton administration was inexperienced and didn’t know what it was doing.
For more information, especially on the military side, please read "Critical Analysis on the Defeat of Task Force Ranger".