There are a number of causes of crime, including the breakdown of the family unit, drugs, a psychological belief system that rejects the legitimacy of the rule of law, and psychopathetic tendencies that lead lead individuals to commit crimes despite knowledge that it is wrong. If one were to put his or her finger on a single underlying cause of crime, however, it would probably be poverty, without which at least some of the aforementioned causes would be far less likely.
There are certain facts that lead to a strong connection between poverty, the absence of a strong family unit, and crime. Teenagers from low-income families, especially where there is only one parent, are statistically more likely to commit crime than teenagers from parents with two families. As the incidences of single-parent families are more prevalent in low-income communities, and since children from broken families are more prone to commit crimes, then it stands to reason that the underlying socioeconomic conditions are the major contributor to crime.
Another factor that again has its roots in poverty is the likelihood that children born of parents who are abusers of drugs or alcohol are likely to commit crimes. Most of the factors that contribute to crime have their roots in poverty, with its correlary of lower levels of education, selfl-esteem, and hopelessness regarding the future. This is not to suggest that all children from lower income environments are prone to criminal behavior; on the contrary, many children rise above their circumstances and pursue meaningful careers. Nor should any of the above be interpreted as an indictment of single-parent families, as there are many perfectly functional such families. It is, however, an indictment of the role that poverty plays in the creation of broken families in which child welfare is seriously neglected.
One of the single largest crime problems in the United States involves gang activity. The single largest recruiting environment for gangs are the low-income neighborhoods in which they take root, and from which there is a steady supply of young, impressionable boys desperately in need of "family" and the guidance and structure gangs provide. Again, absent the sense of hopelessness that permeates many low-income neighborhoods, incidences of gang activity -- i.e., crime -- would be far lower.