one's home country, one's own country
そのスパイは本国へ帰るとすぐに他国へ行くように言われた。
As soon as the spy returned to his home country, he was told to go to another country.
奴はアメリカ生まれで本国の協力で捕まえた
He was born in America, and we caught him with help from his home country.
— GHOST IN THE SHELL (1995)
本国にラピュタ発見の報告をしたか？
Did you report the discovery of Laputa to your home country?
— 天空の城ラピュタ (1986)
彼の音楽は本国では人気がなかった。
His music wasn't popular in his home country.