Union of Kėdainiai
- For the preceding treaty, see Treaty of Kėdainiai
Union of Kėdainiai (or Agreement of Kėdainiai, Lithuanian Kėdainių unija or Kėdainių sutartis; Polish Umowa Kiejdańska) was an agreement between several magnates of the Grand Duchy of Lithuania and the king of the Swedish Empire, Charles X Gustav. It was signed on 20 October 1655 during the "Swedish Deluge", part of the Second Northern War. In contrast the preceding Treaty of Kėdainiai of 17 August, which put Lithuania under Swedish protection, the purpose of the Swedish-Lithuanian union was to end Lithuania's union with Poland, and set up two separate principalities in the Grand Duchy of Lithuania. One of these was to be ruled by the Radziwiłł (Radvila) family, while the rest of the duchy was to remain a Swedish protectorate.
The agreement did not last for long and never came into effect, as the Swedish defeat in the Battles of Warka and Prostki as well as a popular uprising in both Poland and Lithuania put an end both to Swedish power and the influence of the Radziwiłłs.
The Radziwiłł family was the owner of vast areas of land in Lithuania and Poland and some of its members were dissatisfied with the role of the magnates, who in the Polish–Lithuanian political system theoretically had the same rights as the Polish and Lithuanian nobility. Eventually, the interests of the wealthy clan, known as "The Family", and the Crown began to drift apart.
In 1654, during the Swedish and Russian invasion of Poland, known as "The Deluge", two notable members of the Radziwiłł clan, Janusz and Bogusław, began negotiations with Swedish king Charles X Gustav, aimed at dissolving the Commonwealth and the Polish–Lithuanian Union. At that time the Grand Duchy of Lithuania was attacked on two separate fronts by Russia and Sweden, and political control over its area deteriorated. The Lithuanian army capitulated to the Swedes and the state collapsed. Most of the Crown of Poland along with western parts of Lithuania were occupied by Swedish forces, while most of the Grand Duchy (except Samogitia and parts of Suvalkija and Aukštaitija) was under Russian occupation. In addition, the Khmelnytsky Uprising was taking place in Ukraine.
On 17 August, Janusz Radziwiłł signed the Treaty of Kėdainiai, putting the Grand Duchy under Swedish protection. On 10 October 1655 (O.S.), Janusz and Bogusław Radziwiłł signed an agreement with the Swedes at their castle at Kėdainiai. According to the treaty, signed by the two cousins in the name of all Lithuanian nobility, the Polish–Lithuanian Union was declared null and void. In exchange for military assistance against Russia, the Grand Duchy of Lithuania was to become a protectorate of Sweden, with a personal union joining two states. In addition, The Family was to be given two sovereign principalities carved from their lands within the Grand Duchy and the Lithuanian nobility was to retain its liberties and privileges.
The agreement never came into force. Its main proponent, Janusz Radziwiłł, died only 2 months after its signing, on December 31, in the Tykocin Castle, besieged by forces loyal to the King of Poland and the Grand Duke of Lithuania Jan Kazimierz. Shortly after his death, the castle was taken by Paweł Jan Sapieha, who immediately succeeded Janusz Radziwiłł on the office of Grand Hetman of Lithuania. The tide of the war soon turned and a popular uprising in Poland broke the power of the Swedish army. The Swedish occupation of Lithuania sparked a similar uprising in Lithuania. The Swedish defeat and 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 December 31, 1669.
The Radziwiłł family fortunes waned with the next generation. Bogusław became commonly known in Poland as Gnida ("Louse") by his fellow nobles and Janusz became known as Zdrajca (Traitor). Their treason against the Polish–Lithuanian Commonwealth eclipsed the deeds of other members of their family, like Michał Kazimierz Radziwiłł, who fought for the Crown and the Commonwealth against the Swedes.
Although seen as an act of treason by contemporaries, modern views on the proposed Swedish-Lithuanian agreement differ. Some argue that the agreement with the Swedes was made not out of greed and the political ambitions of Janusz Radziwiłł, but rather because of his Realpolitik. According to another theory, Janusz Radziwiłł attempted to get a strong ally against Russia. Supporters of this theory point out that this move was forced because the Grand Duchy of Lithuania lacked the resources to fight a two front war, and the Polish Crown didn't help either with financing or with military forces. Although this choice proved wrong - the Swedes proved to be not much better than Russians themselves.
See also 
- Frost (2000), p. 168
- Frost, Robert I (2000). The Northern Wars. War, State and Society in Northeastern Europe 1558-1721. Harlow: Longman. ISBN 978-0-582-06429-4.
- Kotljarchuk, Andrej (2006). In the Shadows of Poland and Russia: The Grand Duchy of Lithuania and Sweden in the European Crisis of the mid-17th century. Södertörns högskola. ISBN 91-89315-63-4.