The US has a major base in the region. The Combined Joint Task Force (CJTF) has been there for years along with French troops and others. Their base is Camp Lemonier in Djibouti and its purpose is to provide security for the region if conflict breaks out (which it has), Food and Medical aid for the region, water projects etc etc and to get rid of terrorism in the region, which it is doing. Along with that, NATO and the French are also out to sea getting rid of the Somali pirates.
So the US are doing what they are supposed to be doing in the region, stamping out terrorism. Yemen, Ethiopia, Eritrea, Djibouti all contribute troops to the CJTF.