Port action. Currently only flags as a capture.
Using nation laws perhaps players could vote to signal a port sale or port gift.
Perhaps these would require a treaty.
Both sides would need to vote to activate,
Similar to a treaty.
This could also be cancelled.
When a port changes hands under one of these conditions. Global events shows gift or sale instead of capture.
Port action merge. To nations in alliance status,
Could vote to signal merge status.
As ports change hands it shows merge.
Can be set as one nation merging into another.
Or two nation merging into a thrid.