I believe the correct term you are looking for is privateers, not robbers.

They were outside the color of law and often targeted specific trade coming out of adversarial nations.

One kings privateer is another’s thieving pirates.

It depends on who is getting robbed.

Kings and governments just make up special words for when they commit crimes.

Yup - it’s a special kind of outlaw (literally, outside the law) who has a home he can go back to and be protected.