Questions about the past participle and present participle being used as adjective

[polojacky]

When we read "broken heart", it should mean the heart is broken by someone.
China is a developing country. It should mean China is a country which is still developing.
But I feel confused about "America is a developed country".
Does this mean:
(1) America is a country which has already developed.
(2) America is a country which is already developed by Americans.

The reason I feel confused is why country is the subject in active voice when we say "developing country" but becomes passive when we say "developed country". Country develops or country is developed???

Thanks a lot.

 

[SoothingDave]

Because in one case the development is ongoing. In the other, the development is completed.

 

[Raymott]

Country develops or country is developed???

Thanks a lot.

It doesn't matter. When you have a past participial adjective, there's no indication of whether it's active or passive. You need to read that from the context. Given that countries don't develop themselves, "America is a developed country" implies that someone has developed it, ie. that it has been developed by someone. Saying "America has developed" seems to imply that America has developed itself - again, you need to consider the context.