Grammar: America-based or American-based?
When it comes to combinations such as "community-based project", "Sydney-based office" the pattern is noun + -based + noun. The first two words are describing the noun at the end. These are nouns that have no altered adjectival forms.
With nations, however, the adjectival forms are different from the noun forms. Thus, America is the noun and American is the adjective.
However, some people get it wrong with nations and use the noun form when they should be using the adjectival form, so say things – incorrectly – like "America-based company". It should be American-based company, Swiss-based company, French-based company (not America-based, Switzerland-based, France-based etc). Yes, the companies are based in America (not "American") because it is "based in + noun". Move the noun in front of another noun to describe it then it becomes an adjective.
So, the best way to think about it is not to get hung up on the word based but think about how you would use it with other adjectival forms. Therefore:
I have a company.
I have a American company.
I have a American-made company.
I have a American-run company.
I have a American-based company.
You should now be able to see how wrong "America-based company" is. It is just the same as any other adjectival form:
About the author
Jesse Karjalainen is the author of The Joy of English: 100 conversations about the English Language, Cannibal – the language and history of the discovery of the New World, and Roanoke – the language and history of Early Colonial America.