In Renaissance Europe, war and the use of force were regular phenomena and likewise subject of common rules. The theory of ‘just war’, dating back to ancient times, was further developed by legal scholars, and all belligerents claimed to have a just cause, often explained in printed pamphlets. International law consisted of theory and practice, and thus, they should be considered in a mutual context. The focus was still on the question of who had a right to wage war, i.e. on the jus ad bellum, and barely on regulations of warfare or on a containment of war. International law in Renaissance Europe rooted in its very society, in its rules and values. Legal debates and war justifications consolidated the Christian European community, which even in war times did not break apart, even if it was contradictory to the principle of sovereignty and the idea that a sovereign owes no justification to anyone. Moreover, scholars and belligerents argued with natural law and insisted in the universality of international law, although it was in fact basically European. Thus, in Renaissance Europe well-established traditions existed for how to handle war, but they were more and more challenged by the idea of sovereignty, as well as by the European expansion and by global interaction.

This chapter describes territorial conflicts among lords, parishes, cities and towns, and how they contributed to emerging notions of the territoriality of states. It surveys debates regarding both the expansion to new territories and the conservation of existing territories and considers how these debates operated both in Europe and in European overseas colonies. It analyses the writing of jurists as well as a plethora of practices that contemporaries pursued, which despite their obvious local reiterations, were mostly pan-European. Among other things, it covers the question of just war, taking possession of not yet occupied land, discovery, prescription, conservation of the status quo and the role of both conflicts and agreements, including agreements with indigenous peoples, natural law, the law of nations and of relations between territory and jurisdiction. To explain developments during the Renaissance, it observes a much longer time span that began in the Middle Ages and allowed for both slow and revolutionary transformations. It shows that developments in Europe were important, but as vital in both encouraging and empowering change was colonialism, which affected many peoples and territories across the world but also modified Europe in ways we have not yet completely understood.

This chapter charts the profound transformations undergone by diplomacy, both secular and papal, in an age of dramatic intellectual, political and military upheaval. Considering both scholarship and practice, the chapter assesses the rise of ‘resident diplomacy’ and highlights the new structures that were put in place in order to manage longer missions. The investigation of the right to send ambassadors reveals persistent traits of pluralism in early modern Europe, while the plurality of diplomatic envoys and roles is taken into account to make the complexity of the notion of diplomatic status more apparent: this status, in fact, cannot be reduced to that of a fully fledged ambassador exclusively committed to the object of their official mission. Information-gathering, negotiation and mediation are singled out as the most significant diplomatic functions. Changes in the conception of diplomatic inviolability and immunity are also considered, and include the emergence of the idea of extraterritoriality concerning both the person of the ambassador and diplomatic premises.

The Ottomans had a variety of ways of dealing with non-Muslim foreigners. In theory, Islamic law assumed a constant state of war between Muslim and non-Muslim rulers, but in practice, long-term peace arrangements were possible and even common. In terms of diplomacy, the Ottomans’ instruments and peacemaking procedures were similar to those of the West, the Turks likewise building on established customs and practices from the Byzantine period and beyond. The ahdnames were particularly important for international relations; originally unilateral documents, they evolved into more reciprocal instruments, only to become more unilateral again in the second half of the seventeenth century. In theory, peace with unbelievers should be temporary, but in practice, the duration of treaties concluded by the Ottomans reflected their assessment of the likelihood of hostilities resuming; in the case of countries that did not pose any military threat to the sultan’s domains, peace could even be concluded indefinitely. As long as both sides maintained the friendship between the two parties, there was no need to fear the Turks. The interconnected phenomena of slavery and privateering regularly put a strain on this friendship, as men, women and children on both sides were dragged off and sold as chattel. This loss of life and property sometimes led to international incidents, in which the Ottoman authorities made it clear that the basic Islamic parameters of peace could not be ignored with impunity.

The question of whether or not the sea can be owned or controlled has occupied the minds of many over the centuries. The discovery of America by Columbus made the questions of ownership of the sea and how regimes to govern the sea could be created and managed gain importance on a global scale. This chapter discusses the history of the law of the sea from the perspective of ‘Renaissance Europe’, focusing on the ‘battle of the books’ dominated by the publication of Mare Liberum (1609) by Hugo de Groot (Grotius) and John Selden’s Mare clausum (1635). It shows that the concept of the free sea was perfectly compatible with the adjacent or territorial sea both in legal practice and in principle. The idea of the free sea, defended and made explicit by Grotius, was not new but originated in Roman law and its medieval interpretations. Rather than the free sea, mare clausum was the new contribution of early modern thinking on the law of the sea. The concept of mare clausum had been shaped by the division of the world’s oceans between Spain and Portugal based on the papal bull Inter Caetera (1493) and the treaties of Tordesillas (1494) and Zaragoza (1529).

The sixteenth and early seventeenth centuries marked a deep crisis of the international political and legal order of Europe, caused by the Reformation, the emergence of some strong composite monarchies and the discovery of the New World. The chapter maps how the law of nations began to emerge as a new paradigm for the governance of Europe under whose wings rulers, diplomats and scholars attempted to advance claims to an exclusive jurisdiction over international relations by sovereign princes and republics. As such, the ‘law of nations’ functioned as a lever, an argument for power in a period of great clashes between centralising governments, opposing confessions, and regional and local elites, rather than representing a reality. The ultimate success by governments in several important states at the end of the Renaissance was facilitated to a great extent by the patrimonial and transactional nature of the states that allowed to include old, autonomous powers in the machinery of state.

Between the mid-fifteenth and mid-seventeenth centuries, norms on maritime warfare by both private and public actors developed through the intensification of maritime trade networks, European colonial and commercial expansion in other continents, the growing ascendancy of the sovereign state, and the emergence of a distinctive legal scholarship on topics of the law of nations. Although even among European political actors, there was still no general consensus on precise and binding norms governing maritime warfare, the building stones of a normative framework were gradually established which would be integrated from the later seventeenth century onwards into a more consistent body of international law. Prize courts played a crucial role in promoting the principles of such a legal framework, as did state practice on key issues such as blockade, contraband and neutrality.

In the great treatises of Gentili and Grotius, the law regulating the ending of war and the restoration were discussed as the third, chronological and logical part of the laws of war. Their conceptualisation of peace was premised on their conceptualisation of war either as an instrument for the vindication of justice or as the settlement of disputes about right. The chapter explains how these theories, and in particular the latter conception, reflected the practices of peacemaking in peace treaties well, focusing on such major issues as the temporal and spatial dimensions of peace, territorial disputes and the place of communitarian interests in a logic that was geared towards the settlement and appeasement of bilateral disputes over dynastic rights.

In the early modern age, the settlement of disputes between the actors of ‘international’ relations hinged on communication channels and negotiation networks that were meant to limit the recourse to violence. Multireligious Renaissance Europe saw the emergence of the jus gentium – as a distinct, gestating branch of law – and modern diplomacy, perceived as a social and cultural practice used not only by sovereigns, but also by non-sovereign actors – a practice allowing both Europeans and non-Europeans to engage in formal and informal interactions, in state and non-state settings, through the elaboration of common languages, of (verbal and symbolic) communication practices and of shared political and legal cultures. In a belligerent era, which spawned many wars, European diplomacy developed new forms of negotiation that attest to an elaborate ‘art of peace’. By the end of the period, the Thirty Years War ended with the first experience of dispute settlement through multilateral talks involving nearly all European powers in Westphalia (1643-9) and reflecting conflicts that attest to the successive integration of non-European territories in ongoing European dispute. The congress demonstrated both the effectiveness and the limitations of this innovative negotiation model.

In the period of the Renaissance, trade became a matter of legislation and policy. Municipal governments and princes aimed to facilitate trade. International trade relations became increasingly supervised by states. This came in tandem with more treaties. From the middle of the fifteenth century onwards, specialized institutions were created and they increased control over foreign merchants. As a result of growing government intervention, the rules relating to trade were found in bylaws, charters and statutes. Besides those there were customs of trade, which were mostly local. New mercantile techniques, becoming widespread in this period, were maritime insurance, bills of exchange and partnerships of merchants. Insolvency became regulated in the sixteenth century. From the 1500s onwards, rights of hospitality for traders and a right of trade were developed in ius gentium writings. However, due to the mostly local customs and legislation, trade across European countries was far from harmonised. Gerald Malynes proposed a universal custom of trade, but he struggled with the combination of ius gentium ideas with the more factual customs of trade. His views nonetheless laid the basis for later categorisations of commercial law as being customary and transnational.

This chapter examines the development of the law governing warfare on land in Renaissance Europe. In this formative period, the law of war became a central feature of international relations and a distinct legal field. Wars of religion, the growth of the Ottoman Empire, dynastic disputes and the European expansion all contributed to an almost permanent state of warfare. Against this background, in the sixteenth and seventeenth centuries, several scholars contributed to the development of the law of war, responding to the political, religious and cultural turmoil of the Iron Century by elaborating different theories of such law. They derived concepts and principles from medieval theology, canon and civil law, as well as from history, literature and philosophy. The chapter relies on both primary and secondary sources drawing on state and military practice as well as scholarly – legal, historical and relevant military literature. It surveys the major principles of the ius in bello on land, the international law governing warfare including booty, siege warfare and the treatment of civilians and prisoners of war. Rather than describing the distinct contributions of several scholars to the early modern jus in bello – which could not do justice to the works of relevant scholars, especially in the light of recent outstanding works in the field – this chapter adopts an analytical approach focusing on key themes of the jus in bello, analysing and critically assessing the contributions of various scholars to the same.