 The treaty broke down in May 1803 with the start of the War of the Third Coalition.As a part of Napoleon's planned invasion of the United Kingdom in 1803-05, the Irish Legion was to provide the indigenous core for a much larger invasion force of 20,000 earmarked to take Ireland, known as the "Corps d'Irlande".The Legion was established on August 31, 1803 in Morlaix, France.