What is it about human sacrifice that ancient man decided that the gods needed to be appeased by killing innocent people? How or why has the idea of human sacrifice been propagated through various cultures through out the world?

Now, I can understand why ancient man or cultures dreamed up the idea of god or gods; to explain the world as they perceived it, but why did someone have to die? Even sacrifice childern so that you could have rain, or a good harvest. This kind of practice is seen from the middle east to the Inca world and previous cultures before the Inca nation. I have not read anything that would explain this. The other amazing thing is that the people accepted the sacrifical killing as a way of life. How can you accept a god that desires to kill people, or your childern? I do not understand that. Even in the Bible when God asked Abraham to sacrifice Isacc, ( I already know all the theological arguments sooooooo, do not enlight me--- I know) this just seems barbaric to me.

The other side of the coin is that the human sacrifice did not always work, there was drought, famine or whatever, but they kept on with this practice; why? In the Inca world people gave of them selfs willing, from what I have read there was an endless supply of people willing to die for the gods. Why do you have to die for god anyways, how does dying add to the betterment of god? Since god created you, he/she then demands your death for appeasment, rain, or better life for the rest of your family? This whole concept of dying for god I do not understand how it started or why people just accepted it.