Polish–Lithuanian–Muscovite Commonwealth

Proponents of such a union among the Polish szlachta and Lithuanian nobility, including the influential secular thinkers Jan Zamoyski and Lew Sapieha, had listed several arguments in its favour: peace on the turbulent eastern border, a powerful military ally and relatively sparsely-populated territories (compared to the Commonwealth) for colonisation and serfdom.

[citation needed] The proposals then 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.)

[1] Although Moscow was willing to agree to some parts of the proposed treaties (like extradition of crime suspects), it strictly opposed points on religious tolerance (non-Orthodox religions, especially Catholicism, were persecuted in Russia, unlike in Commonwealth, which allowed all faiths to be preached) and free movement of people (according to Polish scholars).

Eventually, the disappointed pro-Ivan faction, represented by Jan Sierakowski, issued a statement in the Sejm: "The Great Prince of Muscovy would be the best choice for king, but because of his silence we are forced to forget him and should not mention him again".

[2] 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-Lithuanian armed intervention, the Polish–Muscovite War (1605–1618).

[5] Finally, the idea returned in the 18th century, when the last Polish king and Lithuanian grand duke, Stanisław August Poniatowski, attempted to save the Commonwealth by proposing a marriage between himself and Russian Empress Catherine the Great.

Taking into account that most divisions of the time, if not dynastic ones, were religious 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.

Thus, while the idea of a Polish–Lithuanian–Muscovite Commonwealth was supported early on by some progressive and secular Polish diplomats, the efforts of the few could not in the end overcome Russian opposition to Catholicism and the fear that such a union would spell Catholic domination over Orthodoxy.