Eli5: Why is “The” used for some countries (The Netherlands, The UK, The USA, The Congo) while most every other country does not? (Kenya, Japan, Canada, etc)

Question

Grammatically the countries seem identical and baffled why these few countries have “the” especially since it’s not like there are many other Netherlands/USA/Congo out there which then demands an article to clarify we are taking about THE USA not just USA.

In: 5344

Answer 1

In germany we have something similar confusing:

Since our Nouns have a gender (der (m)/die (f)/das (n) instead of the) our rivers are female or male.

For example is “der rhein” a Male River, but “die Donau“ or „die Mosel“ are female ones.

I don’t know the exact reason, but I read that it depends on who named the river, if it were the German tribes, the name of the river would be female, and if the Roman’s named it /we kept the Roman’s name, then it would be male.