Remnoids
Buckler stepped lightly as he searched the woods, and as his reflexes took over, his mind slipped into thought. There was a paradox that had left him dumbfounded when he first began hunting: out here in the waste jungles, man’s influence had stopped nearly a century ago, but its technology still reigned: small, self-sustaining beasts that had been created as a weapon of war, things designed for espionage and for ambushes. The greatest advantage is to have nature on your side, and the easiest path to that end is not to destroy or exploit nature, but to bend it to your will.
These things could reassemble themselves from scrap, meaning they were endlessly modular, and with each reassembly they adapted themselves to their new situation. They wiped the South Americans off the map, and then their masters razed it for raw materials. Then the reorganized U.N. destroyed the hive mind which controlled the things. Now nobody could know what went on in the mind of these savage veterans. They simply wanted them dead.