From 2000 to 2012, the U.S. violent crime rate fell over 23 percent. Such an improvement in the social fabric would be cause enough for celebration. But the crime drop of the 2000s followed an even larger decline in the previous decade: 32 percent from 1993 to 2000. The 1990s crime drop (in both personal and property crime) was so sharp and so unexpected that by 2000, most criminologists were predicting that an uptick was all but inevitable. Instead, after a brief pause, the crime fall again picked up steam, extending the longest and steepest crime decrease since World War Two.

America’s two-decades-long victory over crime reversed what had seemed to be an inexorable increase in lawlessness since the 1960s. The murder rate had more than doubled from 1964 to 1974, spiking again in the late 1980s and early 1990s. But just as crime was peaking in 1993, it reversed and went into freefall. The greatest beneficiaries of that crime drop have been the residents of minority neighborhoods, where crime was (and still is) highest and where the bulk of the recent crime decrease occurred.

>>> This Chart Shows the Decline in Crime Over the Years

The fact that the American crime drop encompassed every category of serious violent and property offense makes this transformation virtually unique among Western countries. Particular crimes went down by sometimes comparable amounts in other G7 countries, but those nations experienced increases in other serious offenses. And the fact that crime went down everywhere across America makes the phenomenon particularly puzzling, since crime is a local condition.

Neither liberal nor conservative root-cause theories of law-breaking have fared well over the past two decades. Even though the crime explosion during the booming 1960s should have discredited the liberal belief that economic hardship causes crime, criminologists opined in 2008 that the recession would trigger a crime increase. Instead, the recession accelerated the 2000s crime drop.

Family breakdown also moved in the opposite direction as crime, confounding conservative theories. The black unwed birth rate rose from 66.7 percent in 1990 to 71.6 percent today, and the rate among whites rose from 16.9 percent in 1990 to 29.3 percent today. Meanwhile, crime, especially that committed by blacks, plummeted.

So what happened? No consensus exists. Favored explanations among criminologists include the collapse of the crack cocaine trade, a shrinking youth population, and a better job market, but none of these theories perfectly fit the data. The spread of New York–style policing and increased incarceration are better, but by no means exclusive, explanations for the national crime drop.

New York’s crime decline over the past two decades has been twice as deep as the national average and greater than in every other large American city. The primary reason for New York’s stunning decrease in crime is the city’s revolution in policing. Inaugurated in 1994, this breakthrough featured rigorous data analysis, strict accountability for local commanders, the enforcement of quality of life offenses, and proactive pedestrian stops intended to avert crime before it happens. New York’s crime conquest attracted attention, and by the second half of the 1990s, other departments were holding commanders accountable for the safety of their precincts and using up-to-the-minute crime information to target their resources at crime hot spots.

The national prison build-up also played a major role. The prisoner population increased 400 percent from 1977 to the present, following a deincarceration movement begun in the 1960s. That incarceration build-up would have reached its maximum incapacitative power in the 1990s, as Franklin Zimring points out in The Great American Crime Decline. The effect of the current deincarceration movement on the nation’s crime rate remains to be seen.

On Wednesday, Oct. 29, Heritage Foundation will host an event, “Opportunity in America: What It Means and How It Grows – The 2014 Index of Culture and Opportunity.” Heather Mac Donald will be one of the speakers. RSVP here.