Reason of State
Who created the phrase that allows countries to justify many things under the umbrella of "national interest"?
No, no Pietro Vettori (Petrus Victorius), the 16th-century Italian scholar appointed by Duke Cosimo I de' Medici to teach in Florence even if previously he opposed the Medici rule - You can see a painting of him attributed to Tiziano in his Treatise on the praise and the cultivation of olive trees.
The creator of "Reason of State" (ragion di Stato - read "national interest") was his friend and colleague Giovanni della Casa. This was the clergy, poet, and inquisitor related to the arrest of Protestant preacher Baldo Lupetino (the Lutheran Baldo d'Albona).
Giovanni della Casa wrote about "reason of state" in his "Oration to Emperor Charles V" of 1547 - or 1549, depending of sources - as a political justification for certain actions that deviate from common law or morality for the sake of the state's preservation.
The confusion in attribution comes from the fact that Pietro Vettori edited the works of della Casa after the latter's death (Latina Monumenta).
In any case, ideas around "national interest" were incubating at the time.
- Niccolò Machiavelli touches on the concept in The Prince in 1513.
- Giovanni della Casa made the first written known use of the phrase "reason of state" (1547 or 1549).
- By 1589, the Italian Jesuit Giovanni Botero published his influential treatise on the subject which ended popularizing the term throughout Europe (Della Ragion di Stato - The Reason of State).
These things have always urged me to conduct myself very cautiously in this task: and to attribute little or nothing to conjecture and ingenuity.
Sounds like a good advice. We need to be careful with our incomplete information because we never end learning.