Q: what does gross domestic product measure?
A: GDP is a monetary measure of the market values of all the final goods and services produced in a period of time, often annually or quarterly. They’re commonly used to determine the economic performance of a whole country or region, and to make international comparisons.
At the end of the quotation, when the author says “Island” he refers to England. This excerpt refers to the fact that the English people took a great amount of land as its colonies between the 16th and 18th centuries. The British Empire and its Colonial Department was settled in England, which is and Island.
And the author states that it is absurd that a quite smaller island would govern a continent as big as Africa.
True, post WW2 Japans economy boomed and especially in that time they became a world economic power and today they are still one of the strongest economies in Asia.