Are you asking about the geographical size of the origin of an empire? Are you referring to population?

The definition of superpower is also a bit loose, but if we use the definition from Ian Bremmer,

"A ‘superpower’ is a country that wields enough military, political and economic might to convince nations in all parts of the world to do things they otherwise wouldn't."

Depending on how you classify the composition of the superpower, I would definitely start with Great Britain. The Caribbean was colonized in the 16th century, and from there efforts would expand to The Americas, Africa, Australia, the Middle East and India. The British Empire was the largest in the world.

Again though, the question is difficult due to the term superpower. It was first used during the last years of WW2 to describe the redistribution of power. Nicholas J. Spykman is often credited with developing the term as it is currently defined. Some International Relations experts would maintain that the only superpowers that have existed are Great Britain, the USSR, and the US. Even though an entity such as the Roman Empire could wield great power, truly global reach on a reasonable time scale was not achievable until post-WW2. So the sample size is obviously small.

That depends on your definition of Super Power. The term was invented after World War II to define the United State, Soviet Union, and Britain.

Taiwan was officially recognized as China and held its veto power in the Security Counsel before the 70's.