"This report provides material on the latest crisis in Yemen and the U.S. policy response. [...] After 20 months of war, battle lines in Yemen have hardened. The Saudi-led coalition has retaken the port city of Aden and the lowland areas of southern Yemen (traditionally Sunni). Houthis- Saleh forces remain ensconced in the capital Sana'a and the mountainous highlands of northern Yemen (traditionally Zaydi). In fact, the lines of control now somewhat resemble the previous division of Yemen into two separate countries, a political situation that lasted from 1918 to 1990. [...] Since March 2015, the United States continues to be the largest contributor of humanitarian aid to Yemen, providing $327.5 million in FY2016. On February 11, 2015, due to the deteriorating security situation in Sana'a, the Department of State suspended embassy operations and U.S. Embassy staff was relocated out of the country."
CRS Report for Congress, R43960
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html