It is true that allegiance to a tribe is one handicap to national unity in Africa. When Africa was divided into countries, it did so with little consultation of local people. Instead, Africa was divided into countries by European powers in what was known as the "Scramble for Africa." This meant that national lines often cut across tribal lines. In general, allegiance to a tribe was a stronger tie for people, and this has occasionally been a handicap to national unity in the continent.
President Nixon's policy of measured troop withdrawals from Vietnam was done under his policy of "Peace with Honor" which sought to say that the US was limiting its forces, not surrendering.