The Blockade of Africa began in 1808 after the United Kingdom outlawed the Atlantic slave trade, making it illegal for British ships to transport slaves. The Royal Navy immediately established a presence off Africa to enforce the ban, called the West Africa Squadron. Although the ban initially applied only to British ships, Britain negotiated treaties with other countries to give the Royal Navy the right to intercept and search their ships for slaves. The 1807 Act Prohibiting Importation of Slaves abolished the intercontinental slave trade in the United States but the ban was not widely enforced. From 1819, some effort was made by the United States Navy to prevent the slave trade. This mostly consisted of patrols of the shores of the Americas and in the mid-Atlantic, the latter being largely unsuccessful due to the difficulty of intercepting ships mid-ocean. As part of the Webster–Ashburton Treaty of 1842, it was agreed that both countries would work together on the abolition of the slave trade, which was deemed piracy, and to continue the blockade of Africa. US Navy involvement continued until the beginning of the American Civil War in 1861; the following year the Lincoln administration gave the UK full authority to intercept US ships. Slavery was not abolished in the United States until 1865 when Congress ratified the 13th Amendment. The Royal Navy squadron remained in operation until 1870. United Kingdom involvement Background The Slave Trade Act 1807 stated that: The African Slave Trade, and all manner of dealing and trading in the Purchase, Sale, Barter, or Transfer of Slaves, or of Persons intended to be sold, transferred, used, or dealt with as Slaves, practised or carried on, in, at, to or from any Part of the Coast or Countries of Africa, shall be, and the same is hereby utterly abolished, prohibited, and declared to be unlawful. Under this Act if a ship was caught with slaves there was a fine of £100 per enslaved person. This fine was usually paid by the ship's captain. In order to enforce this, two ships were dispatched to the African coast, their primary mission was to prevent British subjects from slave trading, and also to disrupt the slave trades of the UK's enemies during the Napoleonic Wars. Diplomacy The original 1807 Act only allowed for British ships to be searched and applied only to British subjects. The slave trade on the African coast