What is the capital city of the United Kingdom?

London is the capital city of the United Kingdom because it serves as the political, economic, and cultural center of the country. It is home to significant institutions such as the UK Parliament, the Prime Minister's official residence at 10 Downing Street, and the monarch's official residence, Buckingham Palace. Additionally, London is known for its global financial district and diverse population, enhancing its status as a leading city worldwide.

The other cities listed are capitals of different nations within the UK: Edinburgh is the capital of Scotland, Dublin is the capital of the Republic of Ireland, and Cardiff is the capital of Wales. While each of these cities plays an important role within their respective regions, they do not serve as the capital of the United Kingdom itself.