Why did Song Dynasty write many poems about national subjugation?

The Influence of the Death of the Northern Song Dynasty on the Poetry Creation of the Southern Song Dynasty; The death of the Northern Song Dynasty gave patriotic poets in the Southern Song Dynasty an ambition and an ideal, so they wrote many poems of national subjugation.

We all know that the Song Dynasty in China is divided into the Southern Song Dynasty and the Northern Song Dynasty. At the beginning of the Northern Song Dynasty, the society was relatively stable and harmonious. Later, the invasion of Jin Bing destroyed the Northern Song Dynasty, but the establishment of the Southern Song Dynasty followed. However, due to the weakness of several rulers, they chose to be content with the status quo, which made the politics in the late Southern Song Dynasty even darker. The rulers want to exchange "old coins" for temporary stability and harmony, but forget the great rivers and mountains that have been occupied for many years. Liu Kezhuang, the poet, is the oldest poet in this period and has the highest official position, so he has more feelings for this corrupt and dark court. The poem introduced to you today is a classic of the poets in this period, from which we can see the poet's grief and indignation at the weakness of the rulers.