The Eternal Conflict explained
The war that Sanctuary was never supposed to be part of.
The Eternal Conflict is the war between the High Heavens and the Burning Hells that predates humanity and, in the series' framing, has no natural end.
This is an editorial primer on established series lore, labelled Analysis.
Sanctuary's awkward position
Humanity exists because the conflict produced something neither side planned for. That has always made Sanctuary a strategic object rather than a neutral party - valuable enough to protect, dangerous enough to destroy.
What Diablo V confirms
Two confirmed statements change the shape of the war: Sanctuary is now the staging ground for an assault on the High Heavens, and the population and their souls are used as weapons in that conflict.
Read literally, that is an escalation the series has been circling for decades. The mortal world is no longer the battlefield or the prize. It is the army.
