I'm currently reading Howard Zinn's A People's History of the United States, and he points out (on page 28 of the 2003 paperback printing) that slavery in the colonies was "the most cruel form of slavery in history" because of two factors:
"...the frenzy for limitless profit that comes from capitalistic agriculture; the reduction of the slave to less than human status by the use of racial hatred, with that relentless clarity based on color, where white was master, black was slave."
And while we think sometimes that we already understand what slavery in the American colonies was like, to get a very real first-hand account, I highly recommend that anyone interested read "The Interesting Narrative of the Life of Olaudah Equiano."
"Interesting" is an understatement!
It's an accessible read, it's contemporary to the times, and Equiano experienced not only U.S. slavery, but also Caribbean slavery.