Is Buddhism a religion?

If I can be allowed to redefine religion as a belief in metaphysical ideas, such as reincarnation or other things based on a system of ontological dualism, I would say yes.

But, I don’t think I have to go that far.

I think karma can readily be understood as an impersonal Higher Power/Ground of Being, one that is not worshipped but is nonetheless seen in some way as omnipotent, then it qualifies on that ground, too, in my understanding.

Let’s put it this way. If we call religion a focus on a metaphysical ultimate principal of organization (another way of saying Ground of Being), it qualifies.