Japanese history; history of Japan
Refers to the academic subject or the historical narrative of Japan. Commonly used in school curricula and book titles.
I am studying Japanese history at university.
He is majoring in Japanese history at university.
We learned about the Warring States period in Japanese history class.
She majors in Japanese history.
I have a Japanese history class today.
国史 is a more formal, literary term meaning 'national history' (of one's own country), whereas 日本史 is the everyday, school-subject term specifically naming Japan.
日本史 covers the history of Japan alone, while 世界史 covers world history, so the two are commonly paired as contrasting school subjects.
Compound of 日本 (にほん, 'Japan') and 史 (し, 'history').