In the sentence ‘John Muir led the creation of national parks,’ the term ‘national parks’ should not be capitalized. This is because it is used as a general noun rather than a specific title or name. Capitalization rules dictate that common nouns like ‘parks’ are not capitalized unless they are part of a specific name, such as ‘Yosemite National Park’ or ‘Yellowstone National Park.’ In this context, ‘national parks’ refers to the category of parks in general, rather than a specific park or designation. Therefore, when you are speaking generally about them, it is correct to use lowercase letters.