Perhaps it is an idea to include a country search in the search function? I would like to find for example Renault, Peugeot and Citroën in the USA. Is it possible to add something like this?

You can do that using the search page, in advanced search, and search for cars containing "(USA)" in the "extra info" field.
It would of course work better / be easier if there was a field dedicated to the country.