The general idea of power-control theory is that levels of juvenile delinquency are affected by the structure of the family in which children are raised. The idea here is that boys who grow up in patriarchal family structures are more likely to be delinquent. In a patriarchal family (defied as one in which the father has more authority at work than the mother), fathers have more power. They use that power by exerting more control over their daughters and less over their sons. Therefore, their sons are more likely to commit deviant acts than would be the case in families where the mothers have more power and exert more control over the sons.
From such a perspective, a drop in crime would have to be explained by a change in the family structure in the United States. If crime is dropping, presumably delinquency has dropped as well. If delinquency is dropping, it must mean that families are becoming more balanced. There is less of a power differential now between men and women, making families less patriarchal. This trend is strengthened by the increase in households headed by single women as these households are inherently not patriarchal. As these less patriarchal households become more numerous, more boys are being subjected to greater levels of control. When this happens, they become less likely to engage in delinquent activities and are, presumably, less likely to commit more serious crimes as well.
Thus, the power-control theory would account for a drop in crime by saying that our family structure is becoming less patriarchal and boys are being subjected to greater levels of control within the family.