Yes, it is true that linguists do not know for certain how language was developed by early humans, but they're able to determine that it started somewhere in Africa, due to human migration patterns.
An Invisible Warfare is basically when the victims of an attack are unaware and without warning nor immediate knowledge are being attacked.
Ethnicity is like your culture. Language, race, and religion all play into your background and culture. However, politics are something that govern the country you live in -- they're not necessarily connected to your background. Therefore, politics would be the correct answer.
