Why has Loulan ancient country changed from a vast forest to a desert now?

Loulan was defeated by drought and water shortage, and the ecology deteriorated. The upper reaches of the river were intercepted and diverted, and people had to leave Loulan.

The disappearance of Loulan is related to the north-south migration of Lop Nur.

Loulan was destroyed by plague and disease.

Loulan was defeated by biological invasion. An insect introduced from the two river basins has no natural enemies in Loulan, lives in the soil, can live in the albic soil in Loulan area, and enters the houses in droves. People can't destroy them and have to give up the city.