Gaining points with any nation requires joining their ranks as a privateer or navy officer or joining the Pirate Brotherhood. As long as you serve a single nation, your own relations are tied to that nation. While you can join as many nations as you wish at the same time, this does reduce the points you gain from your actions.
The nations of the world object to any actions against their allies. It is therefore important to keep up-to-date with the tavern news. This may become especially complicated if you serve multiple nations at the same time.
Depending on the situation, you may be committing an unrespectable acts when you capture or sink any non-pirate ships. The following are considered as such by the civilized nations of the world and are listed in order of severity:
You had no Letter of Marque or navy commission and therefore no legal reason for the attack
You were flying a pirate flag
You attacked a nation you were neutral or friendly with
You were flying a flag friendly to the ship you attacked
Depending on the severity of your actions, you may be recognized as a traitor in non-pirate towns. For common unrespectable acts, this may take a while. However, large offences are considered an act of piracy and affect your relations with all nations.
It is always possible to hoist another flag in battle, which could mean the difference between your actions being considered legal or a major act of piracy. It serves to be careful especially when being recognized for flying a false flag.