The renewal of the war between England and France in May, 1803, at first was advantageous to the United States; it precipitated the cession of Louisiana and it gave new employment for American shipping. French West Indian products were freely imported, re-shipped, and exported, thus avoiding the rule of 1756 (§ 85); as a result, the customs revenue leaped in one year from fourteen to twenty millions. In 1805 these favorable conditions were reversed. In May the British admiralty courts decided that goods which had started from French colonies could be captured, even though they had been landed and re-shipped in the United States. Captures at once began; English frigates were stationed outside the port of New York, and vessels coming in and going out were insolently stopped and searched; impressments were revived. In 1804 thirty-nine vessels had been captured by the British; in 1805 one hundred and sixteen were taken; and probably a thousand American seamen were impressed. [Sidenote: Continental System.] On Oct. 21, 1805, the combined French and Spanish fleets were overwhelmed at Trafalgar. Thenceforward England had the mastery of the seas, while France remained supreme on land. Napoleon, who had in 1804 taken the title of Emperor, was determined to destroy English trade with the Continent, and had no scruples against ruining neutrals in the attempt. He resolved upon a "Continental System,"--to shut against the importation of English goods the ports of France and her dependencies and allies, including, as the result of recent conquests, almost the whole northern coast of the Mediterranean, and a considerable part of the coast of the German Ocean and the Baltic Sea. [Sidenote: Orders and decrees.]