Simple as that. Maybe not even all of them.
Wildllings guarding horse fields, Elementals near Shards, Bandits guarding gold mines, whatever.
Doesn't need to be every resource, and doesn't need to be high strength on every guarded node, but just an idea.
You could scale the guards by distance to starting empires, so nearby resources have no guards or weak guards, but resources out in the wilderness have a chance at more/stronger guards.