Why is the background of Shanze management system in the Southern Dynasties the war in the north and the population moving south?

During the Wei, Jin, Southern and Northern Dynasties, there was a long-term war in the north, which caused serious social and economic damage. Farmers in the north were forced to move their families to the south and flood into the south. The population explosion brought too much pressure to the land and mountains and rivers in the southern region, forcing the Southern Dynasties to strengthen the management of mountains and rivers.

To put it another way: a large number of immigrants poured into the south and filled mountains and lakes everywhere, which not only caused property rights disputes, but also caused environmental damage. The government cannot ignore these social problems.