US involvement in Somalia

Here is assistant secretary of state Johnie Carson explaining US role in Somalia.

It's worth your time.

BTW, that part of war in Somalia (phase 4) ended in 2009 with withdrawn of Ethiopian troops and seizure of large part of Southern Somalia by Islamists, primarily al-Shabaab.

Firstly I don't believe Islamic Courts Union would establish sound governance in the country. Simply because they couldn't stop Islamic militia. Secondly They would try to support insurgency in Ogaden and North Kenya. Could you imagine Ogaden as independent state? Small, inland economy surrounded by another impoverished countries. from the other perspectives Somaliland's separatists are utterly convinced they can live without sharia law, so creating government without representatives of most sensible region of country was pointless.

This wasn't unilateral Ethiopian action. African Union has clear stance that current countries shouldn't be divided and some of its members suffered gravely from attacks by organisations originated in Somalia. Noticeably Uganda, which has largest contingent of troops currently in Somalia.

I don't believe anybody is serious about Somali pirates. why not establish naval blockade?

Maybe TFG wasn't good way to go, but ICU won't go anywhere, so they can impose sharia on any new government in the country with or without US support,

Arguably international and Ugandan efforts in Karamoja and Southern Sudan were successful in bringing some stabilization. Arbitrage between Eritrea and Ethiopia or Eritrea and Djibouti was even more successful. Some US diplomats had their role in this affairs.