Canada and the United States share the world's longest undefended border, co-operate on military campaigns and exercises, and are each other's largest trading partner. Canada nevertheless has an independent foreign policy, most notably maintaining full relations with Cuba, and declining to officially participate in the 2003 invasion of Iraq. Canada also maintains historic ties to the United Kingdom and France and to other former British and French colonies through Canada's membership in the Commonwealth of Nations and the . Canada is noted for having a positive relationship with the Netherlands, owing, in part, to its contribution to the Dutch liberation during World War II.