[iraphael]

I was actually wondering what the data considers "immigration". This shows no African countries light up until around the 90s but that's somewhat incorrectly categorizing influx of people into the US as it ignores "forced immigration" (kidnapping for slavery).

[TheCoelacanth]

This visualization starts in 1820, so it misses out on the time period when most slaves were brought into the country. The US banned the importation of slaves in 1808 and made it a capital offense in 1820. Some were smuggled in illegally after that, but not in the enormous quantities that they previously had been.