From 1965 to 1975, the violent crime rate in the United States roughly tripled. This was puzzling to social scientists because the country was generally prosperous. Many explanations of this rise have been advanced. The number of people in people declined during the same period. New procedures to protect suspects' and criminals' rights may have hindered the work of the police. The rising popularity of illegal drugs created a vast business sector that had no recourse to the court system and turned instead to violence to settle disputes.
From the early 1990s, violent crime declined sharply, though not all the way back to the low levels seen in the early 1960s. This decline has also been attributed to a number of factors: more people in prisons; a more stable organization of the illegal drug business; changes in police tactics, such as the "broken windows" emphasis on reducing apparent disorder on city streets.