Final answer:
The transatlantic slave trade was outlawed after 1808 because the U.S. Congress passed legislation in 1807, which took effect on January 1, 1808, to abolish the foreign slave trade. The domestic slave trade within the U.S. grew as a result, with the Upper South selling excess enslaved individuals to the Lower South where demand remained high.
Step-by-step explanation:
The transatlantic slave trade was outlawed after 1808 due to legislation passed by the U.S. Congress. In 1807, Congress abolished the foreign slave trade, a ban that went into effect on January 1, 1808. Importing slaves from Africa became illegal in the United States thereafter. This decision emerged as a result of a compromise between northern and southern states, which barred any attempt to outlaw the slave trade prior to 1808, as stipulated in Section 9 Clause 1 of the U.S. Constitution. Immediately after this provision expired, Congress voted to block the international slave trade. Despite the ban on importation, domestic slave trade within the country continued and even expanded, particularly due to the high demand for labor in the cultivation of cotton in the South.
The domestic slave trade, which involved trading of enslaved people within the borders of the United States, particularly from the Upper South to the Lower South, grew in prominence. States like Virginia and Maryland, which had transitioned from labor-intensive tobacco cultivation to the more profitable wheat production, found themselves with a surplus of enslaved people. Rather than freeing these individuals, many slaveholders opted to sell their excess slaves to regions where the demand for slave labor was still high. This internal market made it possible to continue the