There is an old saying: ten years later, nobody cares, and he is famous all over the world.

It can be seen from this that the ancients studied hard for ten years, that is, they could "know astronomy above and geography (history) below" and win the first prize in the exam. If so, their knowledge should be quite strong, and they should be proficient in geography, history, astronomy and literature, and only need ten years!

From this point of view, if you just want to study history, as long as you are willing to study hard, at most five years is enough!