In December 1806 President Thomas Jefferson presented his annual message to congress and reminded them that Article 1, Section 9, Clause 1 of the Constitution was going to expire.

“I congratulate you, fellow-citizens, on the approach of the period at which you may interpose your authority constitutionally to withdraw the citizens of the United States from all further participation in those violations of human rights which have been so long continued on the unoffending inhabitants of Africa, and which the morality, the reputation, and the best interests of our country have long been eager to proscribe.”

US Constitution: Article 1, Section 9, Clause 1

The Migration or Importation of such Persons as any of the States now existing shall think proper to admit, shall not be prohibited by the Congress prior to the Year one thousand eight hundred and eight…

If I understand this correctly, Jefferson, a slaveholder and President of the United States was telling the people and the Congress that he would welcome a bill that prohibits the United States and her citizens from participating in the African Slave trade.

Congress went to work and passed a statute prohibiting the importation of slaves beginning January 1, 1808, the exact point the Constitution said they could. This was within months of the United Kingdom passing An Act for the Abolition of the Slave Trade.

Beginning in 1820, the United States Navy was regularly deploying ships to West Africa to police the slave trade as were the British. The Webster-Ashburton Treaty of 1842 between the US and the UK settled border disputes and called for an end to the slave trade on the high seas. This resulted in the United States deploying a permanent African Squadron and the Royal Navy increasing its operations against the slave trade.