Many of the sailors they impressed had never been British subjects, and Monroe was tasked with persuading the British to stop their practice of impressment. Monroe found little success in this endeavor, partly due to Jefferson's alienation of the British minister to the United States, Anthony Merry. Rejecting Jefferson's offer to serve as the first governor of Louisiana Territory, Monroe continued to serve as ambassador to Britain until 1807.[54]
In 1806 he negotiated the Monroe–Pinkney Treaty with Great Britain. It would have extended the Jay Treaty of 1794 which had expired after ten years. Jefferson had fought the Jay Treaty intensely in 1794–95 because he felt it would allow the British to subvert American republicanism. The treaty had produced ten years of peace and highly lucrative trade for American merchants, but Jefferson was still opposed. When Monroe and the British signed the new treaty in December 1806, Jefferson refused to submit it to the Senate for ratification. 