If Sanger's intent was to kill nigerians in America, it sure didn't work.... 
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This might come as a shock to you, but most Negros have no connection with Nigeria.
Sanger's Negro Project was directed at people with very dark skin, regardless of their origin.

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Could be Haiti or the Dominican Republic or Puerto Rico. Could be the Congo or South Africa or Gabon or Cameroon.
Could be the Gold Coast, or Algeria, or Mozambique, or Zimbabwe, or Liberia, or Senegal, or Chad, or Tanzania, or Angola, or Botswana, or Kenya, or you name it.
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And as for whether it was effective, try imagining what their population would have been today WITHOUT Sanger's eugenics agenda in action.