Compare us to the UK, but compare like for like. Most of our prison population is comprised of high crime groups who do not exist to any significant degree (35% of the US, 2.6% of the UK) in the UK.
majority of the prison population in the US comprise only 2.4% of the UK.
I'll point out another statistic which doesn't look good for our incarceration rates, regardless of the racial demographic argument you're making:
Half of all persons incarcerated under state jurisdiction are for non-violent offenses, and 20% are incarcerated for drug offenses, in State prisons. Federal prison percentages are higher.
http://en.wikipedia.org/wiki/Race_and_crime_in_the_United_St...
http://en.wikipedia.org/wiki/Demography_of_the_United_Kingdo...
That said, our prison population is still large even after accounting for this, just not as large as the naive statistics make out.