The Ashikaga era is a part of Japanese history.

The Asuka Period is a part of Japanese history, a time when culture and arts greatly developed.

The Muromachi period is a part of Japanese history, a time when many cultural changes occurred.

The Kamakura period was a very important time in Japanese history.

Wave function is a fundamental concept in quantum mechanics.

I am planning to go to Inner Mongolia, an autonomous region of China, next week.

I have been to Outer Mongolia.

I have been to Chicago.

The Paleogene period was a very important time in the history of the Earth.

The Paleolithic is the first era of human history.