Why, when referring to people from different nations in English, do some words end in "ish" while other words end in "an"? Is there an historical reason for this?

by unsubinator

The "ish" ending includes "Scottish", "Irish", "English", "Welsh", as well as "Polish" and "Danish", "Swedish", "Spanish", etc.

And then we have the "an" ending, as in "Indian", "American", "Brazilian", "Mexican", "Venezuelan", and "Italian", "German", "Iranian", "Jordanian", and so on.

Special cases seem to include how people from the Far East are referred to ("Chinese", "Japanese", "Vietnamese"...), some from the Middle and Near East ("Iraqi" and "Israeli"), and of course "Dutch" and "French".

Is there an historical reason for these different endings?

xiaorobear

If you don't get a response here, you should also try posting this in /r/linguistics, where the users have a ton of knowledge of this sort of thing.