I entertain the idea that spirits are real in a similar sense that our consciousness is real. Spirit is an emergent property of humans. When we are angry and vengeful the "spirit" of war is possessing "us". We are not our former self and lose quite a bit of control. This spirit is eternal, contagious, cross cultures.

Our ancestors put a name and images on something abstract but we discarded it because it didn’t fit our modern materialist viewpoint.