Spiritualism is an age-old belief or philosophy or doctrine, which is based on the basic principle that man is a dual being made up of physical and spiritual elements. The physical component, i.e., the body, might wither away at the time of death. But, the spiritual component -- i.e., the soul, spirit, etc. -- continues to exist and thrive, even if in a different world and in a different manner.
Many ardent followers of spiritualism believe that mediums can be employed and used to contact the spirits. They see life after death not as a static place, but as one in which the spirits continue to evolve and thrive successfully.
These two popular beliefs: it is possible to contact the spirits, and they have an edge over the humans, lead spiritualists to believe that one can get useful knowledge, on ethical and moral related issues, and also on the nature of God and the life beyond, from the spirits. And, this knowledge can be used to make the world a better place to live in.
It is a common notion that spiritualism mainly thrives in India. Spiritualism may have found a fertile ground in the mystic and spiritual land of India. But it is widely followed and practiced in almost all regions of the world, including the USA and Europe although in a somewhat different manner.