Superpower refers to a very powerful country in the global spectrum, often the head of a diplomatic or military alliance. The term hegemon is also sometimes used.
In modern times, the British Empire was the world's first superpower, ruling a quarter of the world during a period of 150 years. It declined in power after the Second World War, during which it expended much of its resources to fight the Axis Powers. Another contributing factor was the loss of overseas colonies as they gradually gained their independence in the years leading up to and following the Second World War.
Throughout the Cold War, the United States and the Union of Soviet Socialist Republics were considered the only two superpowers. After the implosion of the USSR in 1991, America emerged as the world's lone superpower, and is to this day the only country to fulfill the criteria of that definition; China, India, Brazil, Russia are however considered to possess the potential of obtaining superpower status in the course of the 21st Century. At this time, strong antipathies between some its members and the lack of a common foreign policy, let alone a real political unity prevents the European Union from achieving anything close to Superpower status.