ASIENTO, or Assiento (from the verb asentar, to place, or establish), a Spanish word meaning a farm of the taxes, or contract. The farmer or contractor is called an asentista. The word acquired a considerable notoriety in English and American history, on account of the "Asiento Treaty" of 1713. Until 1702 the Spanish government had given the contract for the supply of negroes to its colonies in America to the Genoese. But after the establishment of the Bourbon dynasty in 1700, a French company was formed which received the exclusive privilege of the Spanish-American slave trade for ten years - from September 1702 to 1712. When the peace of Utrecht was signed the British government insisted that the monopoly should be given to its own subjects. By the terms of the Asiento treaty signed on the 16th of March 1713, it was provided that British subjects should be authorized to introduce 144,000 slaves in the course of thirty years, at the rate of 4800 per annum. The privilege was to expire on the 1st of May 1743. British subjects were also authorized to send one ship of 500 tons per annum, laden with manufactured goods, to the fairs of Porto Bello and La Vera Cruz. Import duties were to be paid for the slaves and goods. This privilege was conveyed by the British government to the South Sea Company, formed to work it. The privilege, to which an exaggerated value was attached, formed the solid basis of the notorious fit of speculative fever called the South Sea Bubble. Until 1739 the trade in blacks went on without interruption, but amid increasingly angry disputes between the Spanish and the British governments. The right to send a single trading ship to the fairs of Porto Bello or La Vera Cruz was abused. Under pretence of renewing her provisions she was followed by tenders which in fact carried goods. Thus there arose what was in fact a vast contraband trade. The Spanish government established a service of revenue boats (guarda costas) which insisted on searching all English vessels approaching the shores of the Spanish colonies. There can be no doubt that the smugglers were guilty of many piratical excesses, and that the guarda costas often acted with violence on mere suspicion. After many disputes, in which the claims of the British government were met by Spanish counterclaims, war ensued in 1739. When peace was made at Aix-la-Chapelle in 1748 Spain undertook to allow the asiento to be renewed for the four years which were to run when war broke out in 1739. But the renewal for so short a period was not considered advantageous, and by the treaty of El Retiro of 1750, the British government agreed to the recession of the Asiento treaty altogether on the payment by Spain of £100,000.
A very convenient account of the Asiento Treaty, and of the trade which arose under it, will be found in Malachy Postlethwayt's Universal Dictionary of Trade and Commerce (London, 1751), s.v.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)