Why has the crime rate dropped so much over the past 20 years?

Plunging crime rates also debunk conventional wisdom, left and right. Crime’s continued decline during the Great Recession undercuts the liberal myth that hard times force people into illegal activity — that, like the Jets in “West Side Story,” crooks are depraved on account of being deprived. Yet recent history also refutes conservatives who predicted in the early 1990s that minority teenage “superpredators” would unleash a new crime wave.

Government, through targeted social interventions and smarter policing, has helped bring down crime rates, confirming the liberal worldview. Yet solutions bubbled up from the states and municipalities, consistent with conservative theory. Contrary to liberal belief, incarcerating more criminals for longer periods probably helped reduce crime. Contrary to conservative doctrine, crime rates fell while Miranda warnings and other legal protections for defendants remained in place.

On the whole, though, what’s most striking about the crime decline is how little we know about its precise causes.