Edward's claim to the French crown embittered the strife in a most unnecessary fashion. It was an appeal to every discontented French vassal to become a traitor under a plausible show of loyalty, and from first to last many such persons utilized it. It also gave Edward an excuse for treating every loyal Frenchman as guilty of treason, and, to his shame, he did not always refrain from employing such a discreditable device. Yet, as has been already said, he showed his consciousness of the fallacy of his claim by offering to barter it again and again during the course of the war for land or money. But he finally passed on the wretched fiction as a heritage of his descendants, to cause untold woes in the 15th century. It is seldom in the world's history that a hollow legal device such as this has had such long enduring and deplorable results.
In the commencement of his continental war Edward took little profit either from his assumption of the French royal title, or from the lengthy list of princes of the Low Countries whom he enrolled beneath his banner. His two land-campaigns of 1339 and 1340 led to no victories or conquests, but cost enormous sums of money. The Netherland allies brought large contingents and took high pay from the king, but they showed neither energy nor enthusiasm in his cause. When Philip of Valois refused battle in the open, and confined his operations to defending fortified towns, or stockading himself in entranched camps, the allies drifted off, leaving the king with his English troops in force too small to accomplish anything. The sole achievement of the early years of the war which was of any profit to Edward or his realm was the great naval triumph of Sluys (June 24, 1340), which gave the English the command of the sea for the next twenty years. The French king had built or hired an enormous fleet, and with it threatened to invade England. Seeing that he could do nothing on land while his communications with the Low Countries were endangered by the existence of this armada, Edward levied every ship that was to be found, and brought the enemy to action in the Flemish harbour of Sluys. After a day of desperate hand to hand fighting--for the vessels grappled and the whole matter was settled by boarding--the French fleet was annihilated. Henceforth England was safe from coast raids, could conduct her commerce with Flanders without danger, and could strike without difficulty at any point of the French littoral. But it was not for some years that Edward utilized the advantage that Sluys had given him. As long as he persevered in the attempt to conduct the invasion of the northern frontier of France he achieved nothing.