Thomas Hobbes, in "Leviathan" (1651) put forward a conception of sovereignty similar to Bodin's, which had just achieved legal status in the "Peace of Westphalia", but for different reasons. He created the first modern version of the social contract (or contractarian) theory, arguing that to overcome the "nasty, brutish and short" quality of life without the cooperation of other human beings, people must join in a "commonwealth" and submit to a "Soveraigne Power" that is able to compel them to act in the common good. This expediency argument attracted many of the early proponents of sovereignty. Hobbes strengthened the definition of sovereignty beyond either Westphalian or Bodin's, by saying that it must be: