From the Union of Lublin to the Mutual Guarantee of the Two Nations

The purpose of this study is to show changes in the legal and political nature of the alliance between the Kingdom of Poland and the Grand Duchy of Lithuania over the centuries, from the Union concluded in Lublin in 1569, through the so-called ‘coequatio iuris’ of 1697, until the regulations adopted in the Constitution of May 3, and the “Reciprocal Guarantee of Both Nations” crowning the process and passed at the Four-Year Sejm on October 20, 1791. The study uses a wide range of archival manuscript sources, old prints, parliamentary legislation, and also numerous studies using both old and current literature. The main research goal of the study was to show to what extent the changes in the legal nature of the union of the two countries led to their full unification, which was in the past (and sometimes still is) the interpretation of this process in many studies, and to what extent the federalist character of the Polish-Lithuanian Commonwealth was preserved, which is nowadays the dominant view and which the author of this study is a strong supporter of.