Only half of them are: Basil Rathbone, Musetta Vander, Dave Matthews and Charlize Theron, all South African.
Sidney Poitier was born in Miami, of parents from the Bahamas; Peter Williams, Grace Jones and Clifton Jones are all Jamaican.
Of course, black Carribeans are ultimately of African descent, as white Africans are of Dutch heritage; yet both population transfers took place around the time the colonization of America was getting into full swing (Africans to Jamaica at the end of the 1500s, and the Dutch to Africa in the mid-1600s).
And yet, though the first European colony in America, founded in 1498, included both whites (Spaniards) and blacks (slaves) by 1501, today some people still use the term "African-Americans" as though blacks aren't quite real Americans yet. I guess those three years make all the difference.
What got me thinking about all this was a government form with boxes for "White / Hispanic / Asian / African American" in the "Race" section, and I wondered which box Boer immigrants would check.
Wow. It's all really funny actually. I had a bizarre debate with a former coworker who kept insisting that all black people in America shared the African-American experience. My family is from the Caribbean, and my experiences and culture vary greatly from that of those whose heritage is long-established in the Southern slave trade.
The woman argued that our issues were the same. I argued that they were vastly different, especially since people from the West Indies have suffered prejudice and discrimination not only from white Americans, but from African-Americans as well.
Needless to say, the debate ended right there. ;o)