The oldest international treaties of the Grand Duchy of Lithuania, Rus and Samogitia (second half of the 14th century)
Authors: Havrylenko O. A. 
Published: February 2025

The article highlights the processes of formation of a complex of monuments of international law – the most ancient of the treaties of the Grand Duchy of Lithuania, Russia and Zhemaitia, which were concluded during the period when the lands of modern Ukraine became part of the GDL, which gradually began to play an important role since then in contemporary European international relations.
It is noted that during the Middle Ages, the law of international treaties developed significantly. Gradually, the agreements began to be applied more and more often and over time began to occupy one of the important places in the system of international law of that time, in particular, in the practice of international relations of the Ukrainian People’s Republic of Ukraine with other states and quasi-state entities. A certain part of them was recorded in writing, thanks to which modern researchers now have the opportunity to familiarize themselves with the content of these monuments of law.
The article provides a source-based analysis of the Lithuanian-Russian-Polish treaty of 1352, two treaties of 1366 – between the Grand Duke of Lithuania Olgerd, his brothers Keistut, Yavnut and Lubart and their sons, on the one hand, and the Polish king Casimir III the Great together with his vassals - on the other hand, and the special agreement with Lubart, which supplemented the first one. Attention is also drawn to the Lithuanian-Russian-Moscow treaty of 1368 – a peace agreement that ended the first stage of the Lithuanian-Russian-Moscow war of 1368–1372. July 1372. The Treaty of Ljubutsk is a peace treaty that ended the Lithuanian-Russian-Moscow War of 1368–1372. The prerequisites, content and significance of the treaty on the conclusion of the Union of Krebs in 1385 are highlighted. The content of the treaty of Smolensk prince Yuri Svyatoslavovych on the alliance with the Polish, Lithuanian, Russian, etc. king Vladyslav (Jogaila, Yagello) and Grand Duke (viceroy) for Lithuania Skirgaila (September 16, 1386) was analysed, which established alliance relations between the parties and guaranteed the provision of comprehensive assistance to the king. It is emphasized that an important place among the international treaties of the Great Patriotic War of this period is occupied by the Treaty of Ostriv of August 4, 1392 – the treaty that put an end to two wars - the Lithuanian-Russian civil war of 1389–1392 and the war for the Galician-Volhynian inheritance. The Salynas (Sallinwerder) Treaty between the Grand Duchy of Lithuania and the Teutonic Order of October 12, 1398 was also considered. The conclusion that the range of texts of the GDL treaties of the specified period, which have survived to our time in the originals or chronicle lists, is quite limited. Contracts could be not only bilateral, but also multilateral. They had a personal character; the heads of all the most influential states and quasi-state entities of the region (Poland, the Teutonic Order, Muscovy) acted as counterparties to the Lithuanian princes when concluding treaties. All the considered agreements, to a greater or lesser extent, influenced the further state-legal development of the Ukrainian lands that were part of the Grand Duchy of Lithuania, Rus and Samogitia. Some of them led to changes in the form of the state, others became the basis for changes in the legal regulation of civil relations, led to the emergence of new norms of military law and, of course, all these sources significantly contributed to the development of legal regulation of international relations in the region.