ASSISTANT SECRETARY OF STATE FOR AFRICAN AFFAIRS, LINDA THOMAS-GREENFIELD   Assistant Secretary of State for African Affairs, Linda Thomas-Greenfield sits down with host Carol Castiel to preview the purpose and goals of the first-ever US-African Leaders Summit to take place in Washington from August 5 to 6. They also discuss US policy toward Africa including efforts to end the tragic civil war in South Sudan, combat the terrorist group Boko Haram in Nigeria, bring stability to Mali and the Central African Republic, counter China’s nefarious influence on the continent, foster good governance and to fight corruption.