As the report itself says:
For years the U.S. position on Somalia was to only support the TFG via the UN, AU and indirectly. Part of that policy was to ignore and even demonize independent-minded regional actors like Somaliland and Puntland. Meanwhile the aggressive use of outsider actors like Ethiopia and Uganda to directly intercede militarily created [an] unexpected resurgence of armed resistance.
I am not opposed to working through local actors such as Ethiopia and Uganda, but why do all that hard work with its traumatic consequences when there are indigenous building blocks to work with? Indeed, Puntland has always had a policy of eventually rejoining an independent Somaliland.
Subtlety - that's what was missing.
And this is the approach that should have been taken to Afghanistan from the very beginning - build on the pre-existing, tribal building blocks.