However, the chaotic nature of human expansion into space has resulted in two Great Checks: a powerful alien intelligence known as Lord Thezmothete, who prevents humans and other species from exploiting pre-spaceflight civilizations; and the emergence of the Law Machines, intelligent robots that enforce the law in all places. The Law Machines always enforce the letter of the written law, to the extent that several planets were forced to change governments when corrupt or neglectful officials were arrested en masse. Since someone arrested by the Law is never seen again, human colonies are wary about accepting the presence of a Law Machine in their society.