Why is the song Dynasty divided into two periods ---- Northern and Southern song?

The Song Dynasty is indeed divided into two periods: the Northern Song and Southern Song. This division is based primarily on the geographical shift of the dynasty's capital and imperial court due to the invasion and conquest by invading forces.

1. Northern Song (960-1127):

- The Northern Song period refers to the era when the Song Dynasty ruled over China from its capital in Bianjing (modern-day Kaifeng) in central China.

- This period lasted from the reunification of China in 960 until the invasion and conquest of northern China by the Jurchen-led Jin Dynasty in 1127.

2. Southern Song (1127-1279):

- Following the fall of the Northern Song capital, the imperial court and remaining Song forces retreated south of the Yangtze River and established a new capital in Lin'an (modern-day Hangzhou) in southern China.

- The Southern Song period refers to the era when the Song Dynasty continued to rule over southern China from its new capital, Lin'an.

- This period lasted from 1127 until the final collapse of the dynasty to the Mongol-led Yuan Dynasty in 1279.

This division into Northern and Southern Song reflects the geographical separation and relocation of the imperial court during the dynasty due to the loss of northern territories to invading forces.