For instance, if Pillar of Living Flame does enough damage to destroy the last needed Invader and then adds the last Blight to the island, that is a sacrifice victory. If a Ravage in a land adds the last Blight, but then the Dahan retaliate and wipe out the last Invaders for the current victory condition, that is also a sacrifice victory.
However, Ravages are evaluated land-by-land (in an order you choose), so a Ravage in one land can cause a victory before a Ravage in another land can add the last Blight and cause defeat.
You only check at the end of the action tree, so, for instance, Confounding Mists can prevent loss against the Kingdom of England by pushing out a building the moment it is built.