This article examines the interaction between the political elites of the Grand Duchy of Lithuania (GDL) and the Kingdom of Poland in the context of the emergence of the Westphalian system of international relations during the seventeenth century. Applying a systemic approach, the composite-state concept, and the theory of confessionalization, the study investigates how the international environment influenced political dynamics between the Lithuanian and Polish elites. From the moment of signing the Union of Lublin in 1569, the elites of the Grand Duchy of Lithuania sought to affirm their equal status with their Polish counterparts and consistently defended their political interests, particularly in foreign affairs. These interactions intensified notably during the seventeenth century due to significant political and confessional transformations in Europe, culminating during and after the Thirty Years' War (1618–1648), which were institutionalized by the Peace of Westphalia in 1648. The study demonstrates that, despite periodic disagreements between the elites of Poland and the GDL, neither side viewed the other as an adversary. Instead, they were united by a shared constitutional structure, a common cultural identity forged through the process of Polonization in the GDL, and the necessity to uphold the international standing of the PolishLithuanian Commonwealth within the emerging Westphalian order in Europe. The author concludes that the formation of the Westphalian system significantly shaped interactions between the Lithuanian and Polish elites. The international environment of that period fostered integration rather than the disintegration of the two components of the Polish-Lithuanian Commonwealth. Although confessional and political alliances often shifted rapidly and internal disputes emerged regularly, shared external challenges—particularly those posed by powerful rivals such as the Tsardom of Muscovy and Sweden—encouraged the elites of both constituent parts to reconcile their interests and strengthen unity. Thus, mid-seventeenth-century international developments served as a crucial external factor, shaping the political interactions between the Polish and Lithuanian elites and reinforcing internal consolidation within the Commonwealth in the context of the newly established Westphalian international order.
Liudmila Ivonina (Sun,) studied this question.