Why did people sacrifice in ancient times?

The ancients were superstitious about ghosts and gods, believing that after death, the living became ghosts. The ghost world is the same as the real world. A noble who is alive in this world will become a noble in the ghost world after death. In the eyes of the ancients, ghosts and gods were more powerful than the living. Problems and disasters that the living can't solve, such as human life and death, disease, rain or shine, victory or defeat of war, good or bad hunting and so on. We should consult our ancestors through divination and pray for their enlightenment and blessing. Therefore, the ancients worshipped their ancestors and attached importance to sacrifice. Living nobles enslaved groups of slaves and lived a luxurious life. Out of filial piety, they also considered that their ancestors needed slaves to serve them, so they slaughtered slaves and sent them to the ghost world for their ancestors to enjoy.