The Radziwiłł family owned vast areas of land in Lithuania and Poland, and some of its members were dissatisfied with the role of the magnates, who in Poland–Lithuania theoretically had the same rights as the Polish nobility.

He was a favorite of King Władysław IV, from whom he received the position of Lithuanian field hetman, but was an ardent opponent of his brother and successor Jan Kazimierz.

[3] However, the king, wanting to limit Radziwiłł's omnipotence, made loyal Wincenty Gosiewski field hetman and treasurer of Lithuania, and divided the Lithuanian army into two divisions.

[5][3] In the face of the Russian invasion, Radziwiłł refused to take offensive action and demanded that the king conclude a truce with Moscow and enter into alliance talks with Sweden.

But as he was still hoping to establish an alliance between the Commonwealth and Sweden, upon hearing of the ongoing negotiations he set out in the spring of 1655 on an expedition deep into Belarus against the Russian army.

[8] In 1654, during the Swedish-Russian invasion of Poland, known as The Deluge, two notable princes of the Radziwiłł clan, Janusz and Bogusław, began negotiations with Swedish King Charles X Gustav that were aimed at dissolving the Polish–Lithuanian Commonwealth and the Union.

[9] Lithuania was then in turmoil and was being attacked on two separate fronts by Russia and Sweden, and a Ukrainian peasant revolt, known as the Khmelnytsky Uprising, was spilling into the Grand Duchy's southern regions from Ukraine.

[14] Earlier, on August 3, royal secretary Krzysztof Scipio del Campo of Jan Kazimierz arrived in Lithuania, with permission for the Lithuanian lords to enter into truce talks with Moscow and Sweden.

[17] On August 10 in Riga, Magnus de la Gardie accepted the Lithuanian terms brought by Gabriel Lubieniecki but not without changes, taking the Grand Duchy under his protection on behalf of the Swedish king.

And with him 436 people at the Josvainiai convention, among them field hetman Wincenty Gosiewski, castellan of Samogitia Eustachy Kierdej, and Vilnius canon Jerzy Białłozor.

[23] Soldiers who denounced obedience to the hetmans, as well as the nobility of Brest voivodeship, formed a confederation on August 23 in defense of the Fatherland and King John II Casimir in Virbalis, led by voivode of Witebsk Paweł Sapieha.

[26] At the same time, Moscow's deputy Vasily Likhariev arrived in Kėdainiai on August 30, promising to preserve rights, property and religious freedom in exchange for surrender to the tsar.

Field hetman Wincenty Gosiewski was of different opinion, he was ready to make territorial concessions in exchange for the Commonwealth's anti-Swedish alliance with Moscow.

In Lithuania, the king was to be represented by his governor (Magnus Gabriel De la Gardie, later Bengt Skytte with the title of legate), who did not have to be a citizen of the Grand Duchy.

Janusz Radziwiłł signed a private agreement with the Swedes, under which he received large territorial concessions and revenues; his nephew Bogusław similarly, but on a smaller scale.

[30] The signing of the Kėdainiai Treaty strengthened Swedish rule in Lithuania in the short term and weakened the forces loyal to the Commonwealth and John II Casimir.

[32] Its main proponent, Janusz Radziwiłł, died only two months after it was signed, on 31 December at Tykocin Castle, which was then besieged by forces loyal to the King of Poland and the Grand Duke of Lithuania, John II Casimir.

The Swedish defeat and the eventual retreat from the territories of the Commonwealth abruptly ended the plans of Janusz's cousin Bogusław, who lost his army in the Battle of Prostki and died in exile in Königsberg on 31 December 1669.

Their treason against the Commonwealth largely overshadowed the deeds of the next generation's numerous other family members, including Michał Kazimierz Radziwiłł (1625–1680), who served faithfully against the Swedes.

The Grand Duchy of Lithuania lacked the resources to fight a war on two fronts, and the Polish Crown, which now had its own serious problems and could supply only trifling amounts of money and military forces.