People(s)

I hope I'm understanding your question properly.

After examining the dictionary entries for "people" (which usually also contain "peoples"), I conclude that the distinction is probably made to avoid the following sort of confusion:

Compare:

"Mayan and Chinese people built pyramids in ancient times."
"Mayan and Chinese peoples built pyramids in ancient times."

I can't imagine too many ancient people (individuals) who were both Mayan and Chinese, can you (distance being the obstacle to intermarriage that it is)? But I can easily imagine that there was a people (nation, society) that was Mayan, and another people that was Chinese, and that they were each pyramid builders.

Not that the Chinese were notable pyramid builders or anything :)

It may clarify the question.
We never say "People is..." We always say "People are..."
Besides, many of dictionaries say "plural: people
". See Longman for example. Or check this out:
http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=people

I agree with Speedwell. You use "people" when referring to one group of people, like the Chinese people. But, you use "peoples" when you are referring to more than one "people." For example: The Chineses and Mayan peoples built pyramids in ancient times.
Whereas, you would say: The Chinese people built pyramids in ancient times. And: The Mayan people built pyramids in ancient times.

It's like the word "fish." You can have many fish and many groups of fishes.

http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=people

5 plural peoples : a body of persons that are united by a common culture, tradition, or sense of kinship, that typically have common language, institutions, and beliefs, and that often constitute a politically organized group

"People are stupid" is itself technically awkward, though we are used to hearing it. "People" is a collective term, while "persons" refers to individuals. So people are not stupid, persons are stupid.

However, Merriam-Webster acknowledges that "persons" is switched with "people." eg - "salepeople" instead of "salespersons."

Language evolution at work.

Peoples are peoples so why should it be you and I get along so awfully?

Most of the previous posts are on the right track, but there's something that no one has explicitly stated.

The word "people" meaning more than one person, is a plural noun.

The word "people" meaning a group or society with a common culture, history, geography, ethnicity, etc. may actually be used as a singular noun. Thus, "peoples" would be the plural for more than one "people".

Examples:

"We are a people of honesty and integrity"

"Many peoples originally migrated from Africa during early human evolution"

See the usage note at www.dictionary.com

http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=people