The Swedish invasion of 1655 proved a truly catastrophic event. Faced with the capture of most of the Grand Duchy of Lithuania and Ukraine by Russia and its Cossack allies, a significant number of the magnates and nobles in conflict with Jan Kazimierz surrendered to the Swedes almost without a fight. Jan Kazimierz had to flee the country. Yet the severe pillaging visited upon the land by Swedish soldiers and the German mercenaries in their ranks, coupled with their religious otherness (they were Lutherans), quickly sparked resistance from the plebeian masses and the nobility alike. The successful defence of the Jasna Góra monastery, home to a venerated painting of the Madonna (the painting was in Habsburg Silesia during the siege), at the end of 1655 marked a turning point in the war.

The royal court used this event for propaganda purposes when Jan Kazimierz returned to Poland in 1655/1656. Lwów (Leopolis), where the Swedes had not penetrated, became the command centre of resistance against the invaders. It was there, in the city cathedral, on 1 April 1656, that Jan Kazimierz made a solemn vow before the altar of Our Lady of Graces, establishing the Holy Mother as Queen of the Polish Crown and promising remissions for the peasants. By doing so, the ruler sanctioned the religious nature of the conflict with Sweden and made concessions to the commoners, exploiting their zeal in the fight against the enemy. The ceremonial mass at the Lwów Cathedral was celebrated by the papal nuncio, Pietro Vidoni, with numerous dignitaries waiting on the king in attendance. Although the social programme enounced in the Lwów vows was never put into action, they have come down in Polish history as an important symbol of national awakening and unity in the face of external danger.

From January 1569, the Polish and Lithuanian parliaments (sejms) held their debates in parallel, bargaining for a union agreement. The deliberations were acrimonious, but eventually led to the signing, in Lublin, of an act of real union between the Crown and the Grand Duchy of Lithuania. This happened on July 1, 1569.

The Union of Lublin provided for the merger of the two sovereign countries, Poland and Lithuania, into a single unit that became called ‘the Commonwealth [Rzeczpospolita] of the Two Nations’, to be ruled by a single monarch elected jointly by the two nations in free elections. The Rzeczpospolita was henceforth to have a joint Sejm (parliament) and a shared foreign policy. The central offices specific to each of the countries were preserved, as were their respective official languages, armies, treasuries, and judicial systems. A single currency was also introduced – however, it was minted separately in each of the two countries.

At the same time, however, a considerable change occurred within the nobility itself. It found itself under the influence of three important factors: parliamentarianism guaranteed with the Nihil Novi constitution (1505), increased influence of works by Aristotle and Cicero and the actual needs of the state. This gave birth to the so-called Executionist movement, with many outstanding thinkers and statesmen among its supporters. Stanisław Orzechowski (1513–1566), a clergyman and historian, was one of them. He was highly educated, and his rhetoric skills were exceptional, which gave him the nickname of the ideologist of the Nobles’ Golden Liberty.

Orzechowski enumerated the principles of the republican politics in his Appeal to the Polish noblemen, focusing on the law and its meaning for the functioning of the State. Owing to this law, Poland enjoyed such an attractive way of living that even its neighbouring states, such as Ruthenia, wanted to join the Kingdom as a province. It also protected freedom, which was less and less common in other European countries dominated by monarchs’ absolutism. Finally, the Kingdom of Poland, whose political system drew from the ancient mixed governments, enjoyed stability so that the king, the senate or the nobility did not threaten the interests of the whole state.

Orzechowski stated that all of those rights that served Poland so well were gathered and codified by Jakub Przyłuski. Orzechowski’s work was just an introduction to the collection. We could say that if Przyłuski’s Statutes were a legal textbook, Orzechowski’s Appeal was a practical commentary. Thanks to the latter, noblemen could learn that they were not just subjects to the king but also citizens of a free country.

In this context Andrzej Frycz Modrzewski was a unique figure. He not only remained an advocate of equality and a keen fighter for the reform of the penal code as far as punishment for homicide was concerned, but also his horizons were much broader. Written in impeccable Latin, his O poprawie Rzeczypospolitej [on the betterment of the Commonwealth] was a work which undertook to present the state affairs in a comprehensive manner. Its beginning was based on Aristotle’s authority, but the shift in thinking was manifested in the details. Frycz modified Stagirite’s definition and stressed that “all inhabitants of the Commonwealth are obliged to direct all their work, intentions, effort, diligence, and providence towards the benefit of all citizens’ well-being, so that everybody can live a happy life.” This thought then set the direction of the reasoning presented throughout it. The Commonwealth exists because it is bound by law and as the same laws are to govern the state, then criminals should be subject to equal punishment. Thus equality before the law is a consequence of the initial assumption that the Commonwealth exists for the happiness of all its citizens. And the law, which is to serve the state, can vary punishments, but only to the top dignitaries’ detriment because their crimes do more harm to the state than the crimes committed by plebeians.

On the one hand, Frycz’s thought was characterized by great radicalism of opinions and it was difficult to expect that the 16th-century society would accept it. On the other hand, O poprawie Rzeczpospolitej is a pearl of the Old Polish political thought, which in its masterpiece did not forget to plead the lowest class’ cause.

At the turn of the 15th and 16th centuries, the monetary system descended into chaos that was caused by the dynamic process of the debasement of coinage related to, for example, the lack of precious metal in Europe. In his Writings about Money (1526) which were dedicated to the causes of the deterioration of money, the decrease of its purchasing power and social and political consequences of this process, Nicolaus Copernicus made a distinction between the face and intrinsic value of a coin.

Moreover, he stated that if there were two coins with a similar face value in circulation, the coin that had the highest quantity of the precious metal would be supplanted and accumulated. As a result, only the worse coin would remain on the market. Hence, the principle that explains this process, “bad money drives out good”, which, in the economy, is called the Gresham–Copernicus law. Copernicus also noted that “bad money” could have a negative influence on the economy of the whole country and even lead to its fall.

In their analyses of the content of Memoriał and inspiration that stood behind it, historians stressed both: the continuation of Polish tradition of political and legal thought: Matthew of Kraków, Paweł Włodkowic and Jacob of Paradyż and the content, which coincides with the Hussite ideology, inspiration drawn from the works of fourteenth-century French legists, and finally, the possible inspiration by the notion of the fifteenth century German reformers who formed the so-called Reich Reform movement. That is because its author, doctor in Roman and canon law, distinguishing himself from other secular dignitaries of his epoch by his careful education (he studied in Erfurt, Vienna and Bologna), paid particular attention to legal aspects of the functioning of state.

Jan Ostroróg’s Memoriał causes many problems to historians. There were opinions that we do not have the authentic text and we only have an adaptation of an earlier work, prepared specifically for political purposes. On other occasions, there were suggestions that the text is an apocrypha created in the first half of the sixteenth century, in which the name of the Poznań castellan was used to express the postulates dating back to the times when the executionist movement was formed. One of the reasons for doubts is the fact that the oldest manuscripts we have date back to the 30s of the sixteenth century, so they are several decades younger than the time in which the historical figure of Jan Ostroróg lived and acted.

The need for a Polish-Lithuanian union arose in the late fourteenth century around the threat posed to both the Crown and the Grand Duchy by the expansion of the Teutonic Order. The baptism of Lithuania was meant to deny the Teutonic order any pretext for invading the country, to provide the basis for an alliance between Poland and Lithuania, and buttress the rule of the Lithuanian magnates over the Ruthenian population, which was numerically predominant in the Duchy.

Together with all the people of his lands, Jagiełło chose to accept baptism in the Roman Catholic rite, release all Christian captives from Lithuanian bondage, strive to regain the lands lost by the two countries, and also to adjoin [applicare in the Latin text] his Lithuanian and Ruthenian territories to the Crown of the Kingdom of Poland. The latter promise became the seedbed of a dispute between Jagiełło and his first-cousin Witold (Vytautas), who ruled in Lithuania. Moreover, in the following decades this dispute embroiled the Polish and Lithuanian lords, as well. To this day the interpretation of the word applicare remains a subject of controversy between Polish and Lithuanian historians. Polish scholars read the term as describing the intention to incorporate the lands of the Grand Duchy of Lithuania into the Polish Crown, while Lithuanian scholars argue that it expressed the clear intention of maintaining a loose federation of independent states, such as typified the Polish-Lithuanian union until the year 1569.