Violent crime rates may have increased initially during the Depression (the countrywide homicide death rate reached a century high in 1933, at 9.7 per 100,000 people), but the trend did not persist throughout the decade. After rising in most years between 1920 and 1939, the nation's murder rate began to drop in 1940, when it was estimated to be about the same as it had been in 1935.
The number of police officers on the streets decreased by more than 10 percent from 1929 to 1939, so it is no surprise that some observers believed that the decline in murders was due mainly to fewer arrests being made. However, researchers have found no evidence for this theory. The growing popularity of radio may have played a role in reducing violence, since many listeners tuned in at night when crime news was reported. There also were less robberies and assaults near schools and churches, which may have led parents to send their children to school and worship services.
It is clear that overall crime rates were falling even before World War II, so it cannot be said with certainty that this war had a direct effect on violence. But there are several factors that may have contributed to decreases in crime during this era. The use of gasoline additives to improve engine performance may have reduced the force needed to drive certain types of vehicles, such as cars, which would have made drivers less likely to fight one another.
The murder rate was estimated to be more than 30 per 100,000 people in 1700, declining to less than 20 by 1800 and less than 10 by 1900. Crime rates in the United States rose after WWII, peaking in the 1970s and early 1990s. Between 1960 and 1991, violent crime nearly doubled. In that same period, crime rates increased by almost 50% for children under 11 and by about 80% for adults over 65.
The most recent data available (2014) shows that the total number of murders was down slightly from 2013 to 2014, while the national murder rate remained largely unchanged at around 5.5 per 100,000 people.
In terms of race, blacks are disproportionately likely to be murdered. According to the FBI, in 2014 black Americans made up 14% of the population but accounted for 37% of all homicides. Using census data, Philip Martin has shown that between 1980 and 2010, the proportion of blacks aged 10 years or older who were not enrolled in school fell from 91.4% to 84.9%. He also found that among young adults (aged 20-29), black unemployment rates exceeded those of whites by large margins during each of these periods.
There are several factors that may account for this disparity. Many studies have shown a direct correlation between poverty and violence, with poor black communities being up to seven times more likely to experience homicide than affluent white communities.
Property crime increased by more than 75%.
During this time period, cities across the country experienced rising murder rates. Detroit had the highest rate in 1964 with 912 murders per 100,000 people. New York City had the highest rate in 1990 with 641 murders per 100,000 people.
However, some researchers believe that over-punishment of criminals may have also played a role. They say that because prisons are becoming increasingly crowded, judges are handing out long sentences which leads to more inmates than prisons can hold. This creates a "prison pipeline", where prisoners are forced to commit further crimes to pay off their initial arrest. Others say that changes in police practices may have also contributed to higher crime rates. For example, they point to studies showing that the War on Drugs has led to greater use of torture by law enforcement agencies and less cooperation from suspects.
Overall, it is difficult to pinpoint one single cause for the rise in crime during this time period.