What are four causes for the ongoing struggle of African-Americans in the book?
There are probably many answers to this question, but the overarching problem was racism and prejudice, which manifested itself in several ways:
Segregation-- Families from a white neighborhood attempted to bribe the Younger so that a black family would not move in. In neighborhoods with racial integration, there was a reported increase in violence.
Poor living conditions-- Families in black neighborhoods paid more money for bad housing. The Younger Family had roaches and Travis chases a rat in the street.
Assimilation-- Beneatha struggles between staying connected to her African roots and following her dreams of becoming a doctor. George wants her to pursue her dreams of medical school (making her more American), while Joseph Asagai wants Beneatha to dress and act like more African.
Fewer opportunities: Although we want to believe that everyone can achieve the American Dream, it was extremely difficult for African Americans in the 1950s. Walter Younger aspires to achieve part of this American Dream, but he is frustrated at every turn. Although he is willing to work hard, opportunities for him are few because he is black. His culture has relegated him to the servant class. When some money does become available to him, his business opportunities are also few— for few businesses historically thrived in minority neighborhoods.