Chen has marched his army into Vạn…

Chen has marched his army into Vạn Xuân territory by spring of 545 and laid siege and devastation to many cities.

His initial invasion had been stalled by Ly imperial forces for months.

However, in the winter of 545, Chen lays a surprise attack on the capital during the monsoon season.

Ly Nam De's forces are caught off guard and the imperial administration is forced to abandon Long Biên and flee westward into the region of present-day Laos, where communities along the Mekong River have begun to form into townships called muang.