Correct answer: Britain
The Act Prohibiting Importation of Slaves was passed by the United States Congress on March 2, 1807 and went into effect in 1808. The law prohibited any new slaves to be brought into the US.
An Act for the Abolition of the Slave Trade was an act of Parliament in Great Britain, given royal endorsement on March 26, 1807, which prohibited any further slave trade by or within the British Empire.