The presence of U.S. counter-terrorism forces north of Somalia (in Djibouti) apparently played a role is getting al Qaeda to abandon a base in Somalia. Tribal leaders in the "Trans-Juba" region of Somalia (along the Kenyan frontier), appear to have won a battle of wills with al Qaeda. The Islamic terrorists had set up a training camp in the southern part of the region. Tribal leaders began to become concerned that the presence of the Islamist group was luring young men into extremism, not to mention the threat the militants posed to traditional ways and tribal authority (al Qaeda's brand of Islam does not allow for the many adaptations to local custom that have arisen across much of Africa). Then too, there was the possibility that the U.S. or some other power might decide to "do something" about the camp. American counter-terror troops have been operating covertly in Somalia, although the exact nature of those operations has been kept pretty secret (several involved grabbing terrorist suspects, or just meeting with tribal elders or informants).
So tribal leaders arranged meetings where they "invited" al Qaeda to leave. Precisely how this message was delivered is not clear. Nevertheless, al Qaeda has definitely abandoned its main camp in Trans-Juba. Moreover, the site has been systematically destroyed, though whether by Al-Qaeda or tribal militiamen is unknown.