Complex sentence: It was originally used for the Portuguese Empire, the first global empire, since the 15th century, by the Spanish Empire, mainly in the 16th and 17th centuries ant also the British Empire, mainly in the 19th and early 20th centuries.
Split into simpler sentences: It was originally used for the Portuguese Empire, the first global empire, since the 15th century. The expression was then used also by the Spanish Empire, mainly in the 16th and 17th centuries and also the British Empire, mainly in the 19th and early 20th centuries.