As the US slowly tries to shed its title as the world's leader in incarceration, there are some signs that the tremendous gap in incarceration rates between white and black Americans is maybe, finally closing as well.

That finding comes from Keith Humphreys at Stanford University, who wrote about the trend at Wonkblog. Here's a chart that demonstrates his finding, showing the disparity between black and white incarceration rates among men closing by nearly one-quarter since 2000:

But it's not all good news. The gap is still fairly large, although not as large. And as the chart demonstrates, white incarceration has trended up just a little bit since 2000.

So what's behind the trends? Humphreys asked a few criminal justice experts, and they put forward a few theories:

Law enforcement may have remained tough on crime in rural and suburban areas — which are more likely to be white — as police and prosecutors have become softer on crime in urban areas in response to, for example, the Black Lives Matter movement. (The opioid epidemic, which has hit white Americans harder, may have led to tougher attitudes in some rural and suburban areas, too.)

Law enforcement has focused more on sex offenses, which are disproportionately committed by white offenders. Humphreys noted, "Consistent with this explanation, a larger proportion of white inmates have been convicted of sex crimes (16.4 percent) than have black inmates (8 percent)."

More broadly, there are signs of deterioration in white communities across the US — Humphreys pointed to "rising rates of suicide, drug overdose, poor mental health and inability to work" — that could contribute to more incarceration.

So there's some good and bad here: It's good that racial disparities are closing, but it's not good that white Americans are now locked up at slightly higher rates.

Watch: How mandatory minimums helped drive mass incarceration