They didn't.
Do you really believe that?
Yes they did. Before 1808, American ships flying the American flag, crewed by Americans sailed to West Africa, bought slaves there and imported them into the country. The Americans participated in the slave trade. We were not the heavy weight hitters of that trade, only about 2 or 3 percent of slaves were carried on American ships but we did participate. After the importation of slaves became illegal, Americans continued to be involved in the slave trade. Instead of coming to America, the slaves went primarily to Cuba and the other Caribbean islands. Often American slave ships would sail under false flags. In addition to direct participation in the slave trade, American ship yards built ships for the slave trade, American banks lent money to pay for the voyages, and American insurance companies insured the ships and the black ivory they transported.