United Kingdom–United States relations

Relations between the United Kingdom and the United States have ranged from military opponents to close allies since 1776. The Thirteen Colonies seceded from the Kingdom of Great Britain and declared independence in 1776, fighting a successful revolutionary war. While Britain was fighting Napoleon, the two nations fought the stalemated War of 1812. Relations were generally positive thereafter, save for a short crisis in 1861 during the American Civil War. By the 1880s, the US economy had surpassed Britain; in the 1920s, New York City surpassed London as the world's leading financial center. The two nations fought Germany together during the two World Wars; since 1940, the two countries have been close military allies, enjoying the Special Relationship built as wartime allies and NATO partners.

America and Britain are bound together by a shared history, a common language, an overlap in religious beliefs and legal principles, and kinship ties that reach back hundreds of years. Today, large numbers of expatriates live in the other country.

In the early 21st century, Britain affirmed its relationship with the United States as its "most important bilateral partnership" in 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. As of January 2015, the United Kingdom was the fifth largest US trading partner in terms of exports and seventh in terms of import of goods. In long-term perspective, the historian Paul Johnson has called the United Kingdom–United States relations "the cornerstone of the modern, democratic world order".

The two countries also have had a significant impact on the cultures of many other countries, as well as each other. They are the two main nodes of the Anglosphere, with a combined population of just under 400 million in 2019. Together, they have given the English language a dominant lingua franca role in many aspects of the modern world.