What type of was congress prohibited from doing under the constitution until 1808?

In Article 1, Section 9, Congress is limited, particularly, from prohibiting the "Importation" of slaves, before 1808. The slave trade was a bone of argument for many, with some who supported slavery abhorring the slave trade.

The 1808 date (a compromise of 20 years) allowed the slave trade to continue, but placed a date-certain on its survival. Then eventually the Congress passed a law banning the slave trade that became effective on January 1, 1808.

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