<P> British--American relations, also referred to as Anglo - American relations, encompass many complex relations ranging from two early wars to competition for world markets . Since 1940 they have been close military allies enjoying the Special Relationship built as wartime allies, and NATO partners . </P> <P> The two nations are bound together by shared history, an overlap in religion and a common language and legal system, and kinship ties that reach back hundreds of years, including kindred, ancestral lines among English Americans, Scottish Americans, Welsh Americans, Scotch - Irish Americans and American Britons respectively . Today large numbers of expatriates live in both countries . </P> <P> Through times of war and rebellion, peace and estrangement, as well as becoming friends and allies, Britain and the US cemented these deeply rooted links during World War II into what is known as the "Special Relationship ." In long - term perspective, the historian Paul Johnson has called it the "cornerstone of the modern, democratic world order". </P> <P> In the early 20th century, the United Kingdom affirmed its relationship with the United States as its "most important bilateral partnership" in the current British foreign policy, and the American foreign policy also affirms its relationship with Britain as its most important relationship, as evidenced in aligned political affairs, mutual cooperation in the areas of trade, commerce, finance, technology, academics, as well as the arts and sciences; the sharing of government and military intelligence, and joint combat operations and peacekeeping missions carried out between the United States Armed Forces and the British Armed Forces . Canada has historically been the largest importer of U.S. goods and the principal exporter of goods to the USA . As of January 2015 the UK was fifth in terms of exports and seventh in terms of import of goods . </P>

When did the us become allies with britain