Nationalities (plural/generalizations)

To refer to a nation (a group of people from a particular country) we make a noun referring to a single person of that nationality plural by adding the article 'the' and ending '-s' to it.

e.g.: a Brazilian - the Brazilians

Nationalities ending in -ch, -ese, -sh, -iss do not take the ending '-s' in their plural form.

e.g.: a Frenchman/woman - the French

a Chinese - the Chinese

an Englishman/woman - the English

a Swiss - the Swiss.

The mess starts here:

Generalizations.

If you are talking about a specific group (of Russians, etc.), the article 'the' must be used.
Most of the Italians (in this class) are female.
Most of the Japanese (in the restaurant) are from Kyoto.
If you are talking generally, no article or preposition is needed.
Most Americans speak English. Not: Most of Americans

Q1: Why don't we need the article 'the' here? To me it is the same as plural form of nationality since it refers to a group of people from a particular country. I guees all of the examples below are possible and grammatically correct but convey subtle differences in meaning.

Generalizations/plural forms

1. The Russians are friendly.

Russians are friendly.

Russian people are friendly.

The Russian people are friendly.

2. The French are friendly.
Frenchmen are friendly.

3. Spaniards often drink wine. = Spanish people often drink wine.
4. The Chinese enjoy fireworks. = Chinese people enjoy fireworks.

Q2: When we use 'X people', what difference it makes in terms of grammar? Does adding the word 'people' to a singular word denoting to a nationality makes it automatically plural without any need to add the article 'the' and ending '-s'? In theory, it could be a good solution then if you find the whole rule of making plural nationalities complicated or not sure how to make a plural of a particular nationality.