The Polish–Lithuanian–Muscovite Commonwealth was a proposed state that would have been based on a personal union between the Polish–Lithuanian Commonwealth and the Tsardom of Russia. A number of serious attempts, by various means, to create such a union took place between 1574 and 1658, and even as late as the latter part of the 18th century, but it has never materialized due to incompatible demands from both sides.
The proposed union is known in Polish historiography as the Triple Union (unia troista) and has also been called the Polish–Russian Union (unia polsko-rosyjska) or Polish–Muscovite Union (unia polsko-moskiewska). No well-established term for this entity exists in English-language histories.
Proponents of such a union among the Polish nobility, included the then influential secular thinkers Jan Zamoyski and Lew Sapieha, had listed several arguments in its favor: peace on the turbulent eastern border, a powerful military ally and relatively sparsely populated territories (compared to the Polish Crown) for colonization and serfdom. The idea was also supported by the Jesuits and other papal emissaries who never ceased to entertain the idea of bringing Orthodox Russia into the Catholic fold. Some of the Russian boyars found the proposal attractive (like Boris Godunov, a supporter of Tsar Feodor's I candidacy) for various reasons, among them the fact that the Golden Freedoms of the Commonwealth, if applied in Russia, would weaken tsar's power and thus grant the Russian nobility a much higher status than they had enjoyed previously.
The proposals of that time revolved around introducing a personal union between the Commonwealth and Russia, and various economic and political agreements (elimination of trade barriers, free movement of people, etc.), up to the creation of one country, using the framework of that led to the creation of the Polish–Lithuanian Commonwealth in the first place (Union of Lublin of 1569). However all proposals presented by the Polish side were rejected by the Russian tsar. The most promising negotiations took place during 1600, when a Polish diplomatic mission led by Lew Sapieha arrived in Moscow. Sapieha presented to Boris Godunov an elaborated idea of a union between Poland–Lithuania and Russia. The subjects of both rulers were to be free to serve the other ruler, travel to his country, contract marriages with the other ruler's subjects, own land and go to study in the other ruler's country.
Although the Moscow side was willing to agree to some parts of the proposed treaties (like extradition of the crime suspects), it was strictly opposed to points about religious tolerance (non-Orthodox religions, especially Catholicism, were persecuted in Russia, unlike in Commonwealth, which allowed all faith to be preached) and free movement of people (according to Polish scholars). To transform the Russian tsardom into a republic modeled on the Polish–Lithuanian Commonwealth has proven to be a too ambitious project. Many Russians were afraid of polonization, as was already happening with Lithuanian and Ruthenian nobility, and a growing danger stemming from the increasing number of peasant and even noble refugees escaping the Russian Empire, to which Russian tsar Ivan responded with the policy of violent repressions, the so-called oprichnina. Union of Brest of 1596 was a further argument for the Orthodox opponents of the closer ties between Russia and the Commonwealth, who argued that it was the prelude to Catholicization of Russia.
The idea was first broached in the 16th century after the death of the last Polish king of the Jagiellon dynasty, Sigismund II Augustus. Tsar Ivan IV of Russia ("the Terrible") became a popular candidate among the Polish nobility. He had substantial support in Poland, especially among the lesser and middle nobility, who saw in him an opportunity to limit the growing power of the Polish-Lithuanian magnates. During the interregnum, two diplomatic missions (led by Michał Harraburda, pisarz litewski, and Jędrzej Taranowski) were sent from Poland to Moscow to hold discussions. The negotiations failed, due to hostilities resulting from the Livonian War, territorial demands by Ivan (who wanted former territories of Kievan Rus', then under control of Lithuania), and decision by Ivan that Russian side will not 'lower itself to the level of other European monarchies and send a diplomatic mission to Poland begging for him to become a king'. During the second interregnum, in 1574, candidature of Ivan IV was even highly regarded in Poland, however the Moscow diplomatic mission that arrived in Poland had no orders nor prerogatives to negotiate this matter. Eventually the disappointed pro-Ivan faction, represented by Jan Sierakowski, issued a statement in Sejm: ...Great Prince of Muscovy would be the best choice for king, but due to his silence we are forced to forget him and should not mention him again.
The mixed circle of the proponents of this idea saw an opportunity in Russia after Ivan the Terrible, the last Russian ruler of that time whose legitimacy was never questioned, died. The proposal was revived soon after Ivan's death, through the reigns of Stefan Batory in Poland and Feodor I in Russia. After Batory's death in 1587, Feodor I became quite interested in acquiring the Polish throne, and sent a diplomatic mission to Poland. His support among the Lithuanians was high, but Poles issued several demands, among them requiring Fedors's conversion to Catholicism, an absolutely unthinkable event. Eventually Sigismund III Vasa was elected the king of Poland. Death of Feodor prompted Sigismund to propose his candidacy for the Moscow throne, however by the time Polish diplomatic mission arrived in Moscow, Boris Godunov was elected the new tsar.
With the legitimacy issues clouding the entire period of the rule of Boris Godunov, Russia submerged into even greater chaos upon his death, the Russian Time of Troubles, which was accompanied by a decisive Polish armed intervention, or the Polish–Muscovite War (1605–1618), commonly referred to in Russia as the Polish intervention in the end-17th century. In the course of the Polish–Muscovite War, the Polish prince (later king) Władysław IV Vasa was briefly elected a Russian Tsar among other such strange developments like enthronement and short reign of False Dmitriy I, an impostor of tsar Ivan's son. However, Wladyslaw was never officially enthroned and his quick election remained in history as one of the fluke events of Russia's Time of Troubles.
The idea was again proposed in 1656–1658, when Moscow suggested that one of the points of negotiations would be the election of the Russian tsar for the Polish throne. This time it was the Polish side which presented demands (conversion to Catholicism, territorial changes) that eventually discouraged Russians from pursuing this project.
Finally, the idea returned in the 18th century, when the last Polish king Stanisław August Poniatowski attempted to save the Polish state by proposing a marriage between himself and Russian Empress, Catherine the Great.
The very possibility that such an idea could have been seriously considered by the Polish side early on was likely based on the spirit of the 1573 Warsaw Confederation (Warsaw Compact), that guaranteed, at least formally, an equality for non-Catholic nobles in the Commonwealth. However, while the adopted convention was an unprecedentedly liberal act for its time, such full equality was never achieved in reality even within the Commonwealth itself. Taking into account that the most divisions of that time, if not dynastic, were the religious divisions and the relationship between the Catholic and the Eastern Orthodox branches of Christianities were strained at best, it remains surprising that such an idea was seriously considered at all. It remains equally unlikely, that such an idea could have been accepted by the Russian side because the view towards Catholicism in the Russian Empire was highly negative.
Thus, while the idea of a Polish–Lithuanian–Muscovite Commonwealth was supported early on by some progressive and secular Polish diplomats, in the end the efforts of the few could not overcome Russian opposition to Catholicism and the fear that such a union would spell Catholic domination over the Orthodox religion.