The word "voodoo" is derived from the West African word "vodun," meaning spirit. It is not the dark, violent religion, practicing bizzare rituals, painted by Hollywood (which incidentally is where the common name Voodoo came from rather than the more correct Vodun).
Vodun has been practiced in one form or another in Africa for millenia and indeed has probably been around since the beginning of human civilization.
Within vodun teachings there are no accidents - practitioners believe that nothing has a life of its own but rather is intertwined with and interdependent on everything else. Vodun recognises various dieties or Loas, and ancestors play a fundamental part of the traditions being now a part of the world of the spirits, of the Loas.
We have all probably heard of Voodoo dolls and many would view these as evil creations but in fact these dolls are used for many purposes (to attract love, keep someone faithful etc. People do evil, not dolls).