Leibniz's most celebrated apostle was Christian Wolff, a German Enlightenment figure of polymath scope. Born in 1676, he ultimately became the principal apologist for the territorial state and came to regard Frederick the Great as the model of a “philosopher king.” His sympathy for natural religion, a kind of deism, drew criticism from his colleagues at the University of Halle, and when, in a public address in 1719, he pointed to certain non-Christian rulers as exemplary, he caused a public sensation. In 1721 Frederick William I (the father of Frederick the Great) suddenly ordered Wolff into exile on pain of hanging, probably as a result of a campaign against him by the Protestant orthodoxy. Wolff immediately became a figure of European fame, a martyr for the Enlightenment. He took up a new post at Marburg and remained there for some years, despite the remorse of Frederick William and the latter's repeated efforts to bring Wolff back in honor. When Frederick the Great became king in 1740, one of his first acts was to extend to Wolff a generous and public invitation to return to Halle, which Wolff accepted, remaining there until his death in 1756.
Of the leading Enlightenment figures, only Wolff took a particular interest in the law of nations. In his writings, he followed Leibniz. Hobbes and Spinoza had taken the society of nations to be a kind of presocial jungle, replicating at the international level that world of human beings that had existed before the appearance of the absolute sovereign. Wolff accepted that society reflected nature—the nature of human beings. As Leibniz held, however, Wolff believed that it is in the nature of man not simply to preserve himself, but to seek to thrive and mature, to realize a potential to achieve harmony, a potential that is embedded in the possibilities of free will. Therefore the formation of states without a common sovereign, even if it did create a “state of nature” on the international scale, did not create a lawless jungle. Accordingly the interests of any state must include the promotion of this developmental aspect of human beings. In a concept remarkably characteristic of Frederick the Great and of the territorial state, Wolff held that states have fundamental interests derived from their obligation to themselves. These obligations include self-preservation and the development of the human resources of the state. This desire for harmony pre-exists the State and is residually existent also in the society of states. The obligations of one state to other states are nascent, “imperfect,” until they are perfected through treaties.
Wolff expressed this underlying drive for peace in a legal fiction he termed the Civitas Maxima. This Latin neologism was meant to contrast with the term Civitas, which refers to the civil society of a single state. While the Civitas Maxima can be anachronistically misunderstood as a kind of precursor to the League of Nations, it is nevertheless strikingly modern in concept. It might be best explained as a collective unconscious that influences free, self-determining actions. The Civitas Maxima is composed of a body of rules derived from the promotion of the common good. These are not moral rules, but they are rather the source of our evaluation of all rules. Where Grotius thought the contents of natural law could be found in the received traditions of Western practices, Wolff believed that the logical implications of free will—which he saw as the foundation of truth—would provide guidance. These implications would show what states ought to do to enhance their interests, which include a common interest shared with other states. Nature has created a society of states, and the self-preservation of this society also forms an interest of the constituent members of that society.
The Civitas Maxima is a supreme state only in a metaphorical sense, composed of morally equal and free, self-determining states. The law of the “Great State” is composed of what the individual state ought to and would agree to, as well as what states have actually agreed to either by custom or treaty. Thus its laws are based, in every case, on consent, and genuine consent can only be given by free and independent actors. The sovereignty of states, which so bedevils analysts of international law who seek cooperation among states, is instead for Wolff a precondition for law based on cooperation.
Grotius saw in a just war the positive workings of international law: war decided disputes among sovereigns the way litigation decides disputes among citizens. Rights were vindicated by victory. Wolff maintained, instead, that because war could be considered just by both parties, each following his own free judgment, the point of war was the achievement of peace, not simply of justice. Only peace would vindicate the developmental interests of a state, and thus there is no automatic legal right to pursue war in the presence of peaceful alternatives. In domestic societies, not every dispute is solved by litigation, which is an expensive and chancy way to achieve harmony, and harmony after all is an essential element in justice. If, for Grotius and the Westphalian system, victory in war determined the rightness of a cause, for Wolff and the Utrechtian settlement, peace, not war, was the central element in determining rightness. A victor cannot acquire by force of arms a right unless a peace treaty ultimately ratifies that right; this underscores the fact that the assertion of interests, not rights, is the essential duty of the territorial state. Interests are best preserved by consensus, while rights can be vindicated in the costliest and most self-destructive of conflicts.
Toward the end of his life, the fame and drama of Wolff's early career faded. He drew fewer students. His public role had led him to style himself “professor universi generis,” which was bound to invite ridicule. Eventually even Frederick began to avoid him, and on at least one occasion expressed displeasure at Wolff's prolixity. The enormous scope of his master, Leibniz, had degenerated in Wolff's hands into a systematic completeness that was pedantic. Wildebrand referred to him as a “schoolmaster” and pointed to Wolff's “ridiculous micrology.” But though he could not save himself—his renown as a philosopher had vanished by the nineteenth century—he was saved by another, a shrewd and ironic diplomat. Emmerich de Vattel carried Wolff's name everywhere in the pages of Vattel's treatise, the most important and the most widely read essay on international law since Grotius's De Jure Belli ac Pacis.