This command makes one country protectorate another. A protectorate is a country that is protected and controlled by another.
protectorate [country tag] [country tag]
|Country Tag||The country tag of the country you wish to make a protectorate (the county that will be controlled and protected).|
|Country Tag||The country tag of the country you wish to protect/control the other specified country tag. If not specified, this will be the country you are currently playing as.|
Portugal's country tag is POR. This command would make Portugal a protectorate of your current country (your country would control/protect Portugal).
protectorate POR ENG
As we've also specified England's country tag in the above example (ENG), this command would make Portugal a protectorate of England (rather than your current country). See all country tags here.