In 1796, Spain, in alliance with France, declared war upon Great Britain. In 1797, 6000 British troops were sent to help defend Portugal against this alliance. Two years later in 1799, Portugal went into negotiations with France but needed to remain on good terms with Britain as a result of a reliance on the British importation of wine and grain as well as on their naval forces. A failed attempt at invading Spain forced Portugal to conclude the Peace of Badajoz where one stipulation was to exclude the British from the ports of Portugal.