I know this is a grammar forum and not a place to discuss the history of the English language but I know no other place where I can ask a language question.
In the following news report, they talk about a derogatory word for a certain country.
I know there are others, such as "J**" for Japanese and "p***" for people from Pakistan.
But we use "a Brit" for British people and "an Aussie " for Australians.
These are just friendly abbreviations, I think.
No derogation intended.
We call Raymond Ray, Susan Sue and Robert Rob.
We don't mean to disdain them.
You often say "My name is William, but call me Bill"
So, what's the difference between a simple friendly abbreviation and a derogatory term which leads to a boycott of someone or a political problem?
Here is another interesting article. If what the author claims contains some truth, "J**" can be a somewhat friendlier term than "Japanese".