Who contributed to the weakness of the western roman empire?

The western part of the empire fell under the weight of the invasions by the Germanic peoples. The Romans lost political cohesion and fought each other instead of confronting the rebellions. An effective emperor who had made headway against the invaders was deposed and executed in a power struggle. There were king makers and usurpers and the turnover of emperors was high. In the end the western part of the Roman Empire lost all of its lands.