Eli5: What determines if a nationality ends with -ese (chinese, japanese…), -an (Ghanian, Egyptian, American) or just the county itself (Thai)?

Question

Eli5: What determines if a nationality ends with -ese (chinese, japanese…), -an (Ghanian, Egyptian, American) or just the county itself (Thai)?

In: 4879

Answer 1

Nationalities that end with “-ese” and “-an” were given it by European explorers who needed something they could pronounce to call the natives. Countries that have the suffix “-ese” were originally visited by Italian, Portuguese, or French explorers where this sort of suffix is common in their language, such as the Portuguese word “chinês” or even the word “Português” itself. When adopted into English, it became “-ese.”

Whereas countries with the suffix “-an” were discovered by explorers who did not speak languages that commonly had suffixes like “-ese” in their language.

EDIT 1 (Thank you to VeritasCicero for this insight):

As for “Thai,” originally the country was called “Siam” and the nationality was called “Siamese.” They became known as “Thai” of their own volition, and that is the name we started calling them as well. It stands to reason that other irregular nationality names may follow this trend.