Where is sacrifice portrayed in the novel American Gods?

This whole epic tale spins around the idea of sacrifice. The theme is woven throughout the main plot, the crisscrossing sub-plots, and all the other mythology only hinted at in the tale. The gods exist because humans sacrifice their energy and even their lives to them—without the power of human belief, the gods wouldn’t exist at all.

However, gods must make sacrifices as well. Shadow’s horrific nine-day vigil upon Mr. Wednesday’s death is deeply symbolic....

This whole epic tale spins around the idea of sacrifice. The theme is woven throughout the main plot, the crisscrossing sub-plots, and all the other mythology only hinted at in the tale. The gods exist because humans sacrifice their energy and even their lives to them—without the power of human belief, the gods wouldn’t exist at all.

However, gods must make sacrifices as well. Shadow’s horrific nine-day vigil upon Mr. Wednesday’s death is deeply symbolic. Gaiman is using Shadow’s sacrifice as a parallel of the Norse myth in which Odin himself hung on the World Tree for nine days in order to receive the wisdom encoded in the runes.

"Wounded I hung on a wind-swept gallows
For nine long nights, pierced by a spear,
Pledged to Odin, offered myself to myself."

—part of Odin’s speech from the Norse epic Havamal

After this ordeal, Odin supposedly shared the knowledge with humans, and their subsequent worship made him the most powerful being in the Norse pantheon. In effect, his sacrifice of himself as a lesser entity enabled him to give birth to himself as a god, just as Shadow’s death on the Tree revives Mr. Wednesday. (Also, you might want to investigate similarities between Shadow and Baldur, Odin’s son in the ancient lore, and think about how this compares to the Christian story of God sacrificing his own son on the cross.)

One way to think about the theme of sacrifice in American Gods is to notice where it’s absent. The gods are motivated by their desperate need for sacrificial energy, and look at all the trouble and pain it causes. But after the vigil, when Shadow is in the other realm, Whiskey Jack tells him that his people never worshipped their “culture heroes” as gods.

“My people figured that maybe there’s something at the back of it all,” he says, “a creator, a great spirit, and so we say thank you to it, because it’s always good to say thank you. But we never built churches. We didn’t need to. The land was the church” (Gaiman, chapter 18).

Throughout the story, this other realm where Shadow encounters the Native American spirits is presented as a mysterious place where underlying truth can be found. Perhaps Gaiman is asking us to think about whether sacrifice of any kind is actually necessary.