( Answer; )
The existence of four million freed slaves without money, education, or job skills.
( Step-by-step explanation; )
A social problem is an issue regarding a large grouping or community, often one that disrupts the natural order or social norms present. In this case, the 'community' was the United States of America (USA) and the conflict it was dealing with was the recent freeing of slaves, as well as the lack of traditional acquired skills and experiences from the aforementioned due to their previous status.
In other words, following the Civil War, slaves had just been freed. As such, people were having difficulties adjusting to this huge change and the ripples it caused throughout the usual [social] practices.