Apostrophe S

[Mosu]

Hi,

I hope you all having a great day. My question is Why we don't use an apostrophe s in the following?

World leader

American history

Thanks for help

[Qhs922158]

1. Do you think we should say "The Second World's War"? This is an example that shows how the word "world" is used as an abjective.
2. I think the term "American" already means "US's" or "American people's", just like "Chinese history" or "Japanese history".

[Mosu]