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The Peace of Aachen (1748) and the Rise of Multilateral Treaties

By: Randall Lesaffer

In the final months of 1748, the War of the Austrian Succession, which had begun in December 1740 with the invasion of the Austrian Duchy of Silesia by the young Prussian King Frederick II (r. 1740–1786), ended at the peace conference of Aachen [Aix-la-Chapelle]. Unlike the great peace conferences of the two preceding centuries, the Aachen conference did not produce a series of bilateral peace treaties, but a single multilateral treaty between no less than eight powers. Historians of international law generally indicate the Congress of Vienna (1815) at the end of the Napoleonic Wars as the starting point of the emergence of multilateral treaties. However, the Peace of Aachen forms an important precedent to Vienna.

Multilateral treaties were not unknown in early-modern European treaty practice. They were a rather common tool of alliance formation. The ‘Grand Alliance’ whereby Austria, Britain, and the Dutch Republic opposed France and Spain in the War of the Spanish Succession (1700–1713/14) offers a prime example thereof (Treaty of The Hague of 7 September 1701, 24 CTS 11). This treaty started as a bilateral alliance between Britain and the Dutch Republic, to which Austria and other powers were invited to accede. This technique was quite often repeated in the context of coalition policies.

The multilateral peace conferences of the two centuries before 1740, however, all ended in a series of bilateral treaties between the different belligerents. Two explanations can be forwarded for this, the first conceptual and the second practical.

The conceptual explanation derives from the tradition in which early-modern treaty law took root. The doctrinal basis of much of early-modern and modern treaty law can be found in the specific application of general contract law to treaties by late-medieval civilians and canonists. Late-medieval scholars considered treaties between princes to be a particular form of contract. The rise of the sovereign state in the 16th and 17th centuries went a long way to dissociate public treaties from private contracts and did away with much of their personal character. Nevertheless, some features remained. The focus on the strictly reciprocal character of the rights and obligations of parties was one that long endured. For this, bilateral conventions were an appropriate form.

The practical explanation pertains to legal techniques of war- and peace-making. As little as the customary use of the singular—the Peace of Westphalia, the Peace of Utrecht—for the great peace settlements of the early-modern age reflects the underlying legal reality, just as little does the use of the singular for the preceding wars—the Thirty Years War, the War of the Spanish Succession—reflect the legal practice of war. From the legal perspective, these wars did not constitute a single, integrated war between multiple belligerents, but a series of bilateral wars. This did not mean that each single member of a certain coalition would individually declare war on each of the members of the opposing coalition. In most cases, the picture was more complex to the extent that not all members of the one coalition were necessarily at war with all members of the other. The picture was further blurred by the distinction between full belligerents and auxiliaries. The latter were powers which were not formally at war but, usually under the obligations of an alliance treaty, one-sidedly supported one or more belligerents, with resources, money, or even troops. Moreover, the concrete legal implications of the state of war generally differed among ‘pairs of belligerents’. During the war, belligerents took hostile measures against their enemies such as trade restrictions, general reprisals, or confiscation of enemy property, which could and would greatly vary per case. As peace treaties had to deal with the consequences of these measures, specific regulations for each pair of belligerents were necessary. This was also true for the regulation of future peaceful relations, mainly regarding trade and navigation. During the 17th and early 18th centuries, when peace-making practices were not yet well-developed and standardised, this would have made the use of multilateral treaties unpractical.

As the 17th century progressed and the 18th century began, the use of series of bilateral peace treaties also reached its limits. The peace treaties produced between Westphalia (1648) and Aachen show a steady rise of techniques to link separate peace treaties together. One technique was to include the same or similar clauses in separate treaties. This was the technique used for the Peace Treaties of Münster and Osnabrück of 24 October 1648 (1 CTS 271 and 1 CTS 119) which together constituted the Peace of Westphalia. Another technique was the insertion of one peace treaty into another in order to require a power which was extraneous to the inserted treaty to guarantee the implementation of that treaty (e.g., Art. 24 of the Franco-British Peace Treaty of Utrecht of 11 April 1713, 27 CTS 475). Both techniques were primarily designed to ensure the coherence of coalitions.

The choice of a single multilateral peace treaty at the conference of Aachen was likewise dictated by coalition policy. Ironically, it was the dissent rather than the unity within the two opposing coalitions that caused this result.

In the end, eight European powers would accede to the Peace of Aachen of 1748 (38 CTS 297). On the one side there was the ‘Grand Alliance’ of Austria, Britain, and the Dutch Republic, plus Sardinia. On the other side stood France and Spain, with Genoa and Modena as auxiliaries to Spain. Some other auxiliaries, such as Russia on the part of Austria, were not involved in the peace treaty. Prussia, which had already made its peace with Austria at Dresden on 25 December 1745 (37 CTS 429), was represented at the conference but adhered to a strictly neutral course and was not a party to the treaty.

The dynamics and pace of the peace process, which had already begun with a prior conference at Breda in 1746, were determined by the war-weariness of the three major powers, Austria, Britain, and France. London and Austria were so eager for peace that both were willing to make separate peace treaties with France. This put Versailles in the driving seat as it could choose which enemy power with which to compromise first. It chose Britain. In close cooperation with the Dutch Republic, Britain negotiated with France, first at Breda, and then at Aachen. While this allowed both Versailles and London to pressure their chief allies, Madrid and Vienna, into making major concessions, both leading powers preferred to avoid dropping them altogether by making a separate peace treaty. To perform this delicate balancing act, the two leading powers selected a legal technique which reflected these opposing concerns.

On 30 April 1748, France, Britain, and the Dutch Republic signed a preliminary peace treaty with one another (38 CTS 237). More than being a mere compromise among these three powers, the treaty stipulated the conditions for a general peace. It contained many stipulations which directly pertained to the rights and interests of the other powers, such as the guarantee of Austria’s cession of Silesia to Prussia and the cession by Austria of the Duchies of Parma, Piacenza, and Guastalla to the Spanish prince Don Felipe (1720–1765). By showing their allies that they were ready to make peace among themselves, Versailles, London, and The Hague thereby threatened them with the nightmare that they might need to continue the war on their own and thus arm-wrestled them into swallowing major concessions. In the weeks to follow, Austria, Sardinia, Spain, and Genoa acceded to the preliminaries.

The same two-phased path was followed to attain final peace. The actual peace treaty, dated 18 October 1748, was styled as a true multilateral peace treaty between eight equal treaty partners all of which were fully bound to the treaty in its entirety. But again, France, Britain, and the Dutch Republic forced the pace by running ahead of the others. On 18 October, they were the only powers to sign the treaty, with the other five powers acceding later.

The multilateral character of the treaty was considered a novelty. The treaty negotiators understood full well that it squared badly with the underlying legal realities of war. The preamble to the treaty expressed this clearly where it grouped into two separate clusters the different, bilateral wars which together constituted the War of the Austrian Succession. On the one hand there was the cluster of wars which opposed France to the three powers of the Grand Alliance. On the other hand there was the cluster which opposed Spain and its auxiliaries Genoa and Modena to a coalition of Austria, Britain, and Sardinia, with the Dutch Republic acting as a British auxiliary. The distinction between these two ‘wars’ or rather clusters of war was not reflected in the treaty itself as all clauses bound all parties. This was made possible since the stipulations which referred to the legal regulation of the consequences of the war and of future peaceful relations were kept to a bare minimum by reverting to previous peace agreements (Art. 3). Moreover, the standardisation of certain legal technicalities of peace-making, such as the rules of amnesty, restitution, and the release of prisoners of war, had reached such a level that general references to these standard practices sufficed, making detailed regulations for each party unnecessary.

The Peace of Aachen did not cause an immediate overhauling of peace-making techniques among European powers. Whereas the Peace Treaty of Paris of 10 February 1763 (42 CTS 279), which ended the Seven Years War between Britain, France, and Spain, was a multilateral treaty, later peace treaties of the 18th century, such as those ending the American War of Independence in 1783, were not.



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