I learned some knowledge about ancient world history in junior high school, but I have forgotten a lot in senior high school. So I think it is necessary to learn it again and understand the profoundness of the ancient world. But, indeed, high school doesn't study ancient world history. I think there are three reasons:

First, three years of high school, relatively speaking, time is tight, the schoolwork is heavy, and there is no time to study.

Second, the ancient history of the world is relatively unimportant. The book "Global History" does not involve ancient history, but starts with the opening of new sea routes in 14 and 15 centuries.

Third, the ancient world is a divided history, and the whole world is not a unified whole. After the opening of the new route, the world gradually connected and became a whole.