This is the 14579th most frequent Korean word.
미국인도
"미국인도" means "Americans too" or "Americans also."
In this sentence, '미국인도' (also Americans) is used to express that Americans are also included in the group of people whose music the speaker likes.
저는 미국인도 음악을 좋아합니다.
I also like music from Americans.
Here, '미국인도' (also Americans) is used to indicate that Americans are included among those who can learn Korean.
미국인도 한국어를 배울 수 있어요.
Americans can also learn Korean.
In this usage, '미국인도' (even Americans) emphasizes that understanding Americans might have been somewhat challenging, yet he managed to do it.