Why were the song dynasties divided in to two periods - the norther song and the southern song?

The Song Dynasty was divided into two periods—Northern Song (960-1127) and Southern Song (1127-1279)—due to territorial changes following invasions. The Northern Song capitalized on economic and cultural prosperity in northern China, but faced military pressure from the Jurchen tribes, which ultimately led to their conquest of the northern territories. After this, the Song court retreated south, establishing the Southern Song, which continued to thrive economically and culturally despite being reduced in territory. This division reflects significant shifts in political power and regional dynamics during the dynasty's history.