Determiners for Proper nouns?

[Linguistica]

Hello,
I give tutoring and told my "pupils" not to use determiners before proper nouns, because I read this rule somewhere.
But later I thought of some examples and got a little bit confused.

I would not use a determiner in this sentence:
Britains don´t like pie.
*The Britains don´t like pie

but I would use one in this example :

When the Britains attacked,..
*When Britains attacked,..

It seems to me as if you shouldn´t use a determiner when talking about the group of people/things in general.
->Britains don´t like pie.

But in the other example, you are refering to some of them and therefore you should use a determinative?? I don´t really know how to explain it to the children.

Does anyone know where I could find information concerning this topic?
Or does anyone know how to explain the rules?

Thank you very much!

Have a nice day!

[Alan]

Your query seems to relate to nationality nouns rather than proper nouns in general, and so I'll confine my answer to that type.

The use of the definite article before a plural nationality noun for general reference depends on the way that plural is formed: essentially, if it is a true noun (i.e. it takes a plural -s), then the form without article is used, e.g.

Britons* aren't good at foreign languages.

Sometimes Pakistanis don't get on well with Indians.

(*Note the spelling!)

However, if it is merely an adjectival noun (i.e. does not add -s), then the article is required, e.g.

The English aren't good at foreign languages.

Sometimes the Spanish don't get on well with the Portuguese.

One exception to this general rule is forms ending in -ese, which, despite being adjectival, are occasionally found without determination, e.g.

Sometimes (the) Chinese don't get on well with (the) Japanese.

I trust these notes will be of some help!