TANZANIA – The U.N. humanitarian chief is hoping a major ministerial meeting Tuesday will not only raise $1 billion for the three countries at the epicenter of a humanitarian crisis in Africa’s Sahel region but also spur leaders to address the underlying causes, including increasing conflict and insecurity, weak governance and a lack of development.Undersecretary-General Mark Lowcock said in an interview with The Associated Press that the troubling situation in Burkina Faso, Mali and Niger is a symptom “of failure to deal with all of those causes of problems” as well as rapid population growth and climate change.As a result, he said, “we have a record number of people, more than 13 million, needing humanitarian assistance across the border.