In response to Emma's question...

Malawi is no different than any other place in the world in this matter. Wealth tends to accumulate in cities because that is where business occurs. Compare the differences here in the United States between financial centers like New York and Boston against rural communities like Fairbury, Nebraska (they make really good hot dogs.)
Small towns, in general lack major financial institutions i.e. companies, businesses, stores, etc... rural communities also tend to lack health care facilities/hospitals which can make conditions even worse. Without business, there is little money. With little money, there tends to be fewer health facilities. Unfortunately in Malawi, rural areas have a greater need due to the AIDS crisis, thus it is a crisis.
Cities throughout even ancient history are wealthy because that is where wealthy business people live. It's getting them to share it that makes the difference.