Aggression before Versailles

The roots of aggression as a concept of international law are rarely traced back beyond the end of World War I. The Versailles Peace Treaty of 28 June 1919 and the Covenant of the League of Nations, which constituted its first 26 articles, are often quoted as the first seminal steps towards its emergence as a key concept of the modern jus contra bellum. In this article, this assumption is tested and read against the backdrop of 18th-and 19th-century use of force law. The paper makes three claims. First, although international use of force law underwent important change during the 19th century, it remained deeply rooted in the jus ad bellum of the early modern age, which in turn had its roots in late-medieval scholarship. Therefore, 19th-century doctrine and state practice cannot be fully appreciated without an awareness of the historical tradition they built on. Second, although it cannot be denied that 19th-century international law conceded to states the right to resort to force and war, this right was conditional and restricted. Third, both early modern as well as 19th-century international lawyers referred to a concept of aggravated violation of jus ad bellum which -at least in theory -triggered reaction and even sanction by the international society of states against the perpetrator. This was, from the 18th century onwards, loosely and inconsequentially, but with increasing frequency, referred to as 'aggression' or 'aggressive war', both in diplomatic practice as well as in legal scholarship. Although the Versailles Peace Treaty broke with existing peace-making practice and returned to a discriminatory conception of war by blaming the war on Germany and its allies and by sanctioning them, it drew on a pre-existing conception of aggression as a violation of use of force law.