The export of grain from Britain, particularly barley and wheat, was an intermittent trade in the Middle Ages and the early modern period, depending on abundance and scarcity at home and regulated by the corn laws. These laws obstructed the export of corn for longer periods than they allowed it. The most important granary was East Anglia, and the largest foreign market was the Netherlands. King's Lynn and Yarmouth were the principal ports which supplied London, the north, and the midlands. The East Anglian export trade was occasionally allowed by special licences, and at other times was the result of smuggling. Other parts of eastern and southern England which were important exporters of grain were the East Riding of Yorkshire, Lincolnshire, the Downs of Kent and Hampshire, and south Devon. The efficiency of the distribution system allowed some farming regions to import all their corn and thus to concentrate on the production of their own specialities, e.g. cheese (see fairs; markets). The government encouraged corn exports from 1654 and helped the growers of grain by the payment of bounties from 1674. The export trade in grain expanded remarkably in the first half of the 18th century. See David Ormrod, English Grain Exports and the Structure of Agrarian Capitalism, 1700–1760 (1985). From the late 1760s, however, Britain became a net importer of foreign grain. The war with France from 1793 to 1815 caused hardship. The corn laws kept prices high until their repeal in 1846. American grain began to be imported into Britain in large quantities in the 1870s. See the volumes of The Agrarian History of England and Wales.