The Italians came up with this as a result of the need to maintain the delicate balance of power that emerged toward the middle of the 15th century. It was vital for Venice, Florence, Milan, Rome and Naples to keep track of one another and of one another's machinations at foreign courts.
Modern international relations would be impossible without this institution. Its origins are very much bound up with the historical conditions of the later 15th and early 16th century.