There is the Western Han Dynasty and the Eastern Han Dynasty; Western Zhou Dynasty and Eastern Zhou Dynasty; Why are the Southern Song Dynasty and the Northern Song Dynasty not called Northern Song Dynasty and Northern Song Dynasty? The capital of the Western Han Dynasty is Chang 'an (now Xi 'an) and Luoyang, the capital of the Eastern Han Dynasty. Haojing (now near Xi 'an), the capital of the Western Zhou Dynasty, and Luoyi (now Luoyang), the capital of the Eastern Zhou Dynasty. The relative position is the east-west direction. Lin 'an (now Hangzhou) was the capital of the Southern Song Dynasty, and Bianjing (now Kaifeng, Henan) was the capital of the Northern Song Dynasty. The relative position is in the north-south direction, so the Song Dynasty is not called East-West Song, but North-South.