Alma 42:14

And thus we see that all mankind were fallen, and they were in the grasp of justice; yea, the justice of God, which consigned them forever to be cut off from his presence.

All people had fallen. They were caught by what’s fair. God’s fairness meant they would be cut off from him forever.

All humanity had fallen. They were in the grip of justice—God’s justice, which would cut them off from his presence forever.