What role did vassals play in the Warhammer 40k 7th edition universe?

In the Warhammer 40k 7th edition universe, vassals were individuals or groups who pledged loyalty and service to more powerful factions, such as Space Marine Chapters or Imperial Guard regiments. Vassals provided support, resources, and manpower to their overlords in exchange for protection and guidance in battle. They played a crucial role in expanding and maintaining the power of their masters in the grim darkness of the 41st millennium.