On April 7, 1862, the governments of the United States and Great Britain signed an agreement to end the transatlantic slave trade. In some ways this was unusual; both had already had laws on their books that forbade their citizens from carrying enslaved captives from Africa, dating back about half a century. The difference lay not in the ban on slavery but in the cooperation between the two nations. The United States had banned transatlantic trade in slaves in 1808 as part of its Constitution. Great Britain had made significant efforts to restrict the international trade in slaves within its empire in 1807, during the Napoleonic wars.