Intellectually one of the greatest men of his age, Grotius was no less outstanding in the statesman-like nobility of his mind and spirit. As a brilliant classical scholar he produced notable contributions in philology, theology, and history; in his early youth he wrote three dramas in Latin. During his later years he tried to devise a basis for the unification of the warring Christian nations. His De veritate religionis Christianae (1627), which was written as a treatise of common Christianity, became a popular text in Protestant theology in many lands. In his Via et votum adpacem ecclesiasticam (1642) he suggested a method of unification. Also noteworthy were his commentaries on the Bible (later confirmed by critical studies), his Annales et Historiae de Rebus Belgicis (1657), and his textbook on Roman Dutch law.
The continuing fame of Grotius, however, derives from his De Jure Betti et Pacis (1625), which laid the basis for international law. Concerned about the unbridled sovereignty of the national states, the author set out to find some basic universal law to which all alike were subject. He founded his system on reason and the nature of man as a social being, which are summed up in the law of nature. Since all nations are subject to this natural law there is no legal justification for international anarchy. Although Grotius did consider natural law as fundamental, he regarded the existing practice of nations as the best evidence of what the law actually was during his time.