Final answer:
Bahrain declared independence from the United Kingdom on September 3, 1971. It is noted for being the first Muslim nation to host the FIFA Men's World Cup in 2022 and for its democratic reforms post-independence.
Step-by-step explanation:
On September 3, 1971, the country that declared independence from the United Kingdom was Bahrain. This small archipelago, located in the Persian Gulf, has been working towards democratic reforms since its independence.
Bahrain holds historical significance as the first Muslim nation to host the FIFA Men's World Cup, which it did in 2022. While the country is home to a significant Shia population, it has oil wealth and has been experiencing democratic changes, such as holding elections, releasing political prisoners, and allowing women to vote.