Translate the following English sentence to French:
"Possibly the most important founding principle of the European Union was peace and those who seek to join the Union must try to conduct their domestic and their foreign affairs in as peaceable a fashion as possible."
La paix est peut-être le principe fondateur essentiel de l'Union et les pays qui souhaitent en devenir membre doivent essayer de gérer leurs affaires nationales et internationales de façon aussi pacifique que possible.