What did congress make illegal in 1807 in regards to slavery?

In 1807, Congress passed a law that made the importation of enslaved people into the United States illegal, effective January 1, 1808. This legislation was part of a broader effort to curb the transatlantic slave trade, although it did not end slavery itself within the country. The law aimed to reduce the influx of enslaved individuals, but illegal smuggling continued for many years thereafter.