Swedish Lithuania in the context of Dominium directum et utile

The Northern War of 1655–1660 was fought between Sweden and the Polish–Lithuanian Commonwealth, with participation at different times by Russia, Brandenburg-Prussia, the Habsburg monarchy, and Denmark–Norway. It ended with the treaties of Copenhagen and Oliva in 1660.

In 1655, Charles X took advantage of the Russo-Polish War (1654–67) to over-run western Poland. The Grand Duchy of Lithuania was annexed by Sweden, and John II Casimir Vasa took refuge in Vienna. He managed to regain parts of his kingdom in 1656, and the conflict widened when Russia declared war on Sweden, supported by Emperor Leopold and Frederick III of Denmark.

The Union of Kėdainiai or Agreement of Kėdainiai (Lithuanian: Kėdainių unija, Swedish: Kėdainiai förbund) was an agreement between magnates of the Grand Duchy of Lithuania and the king of the Swedish Empire, Charles X Gustav, that was signed on 20 October 1655, during the Swedish Deluge of the Second Northern War. In contrast to the Treaty of Kėdainiai of 17 August, which put Lithuania under Swedish protection, the Swedish–Lithuanian union's purpose was to end the Lithuanian union with Poland and to set up the Grand Duchy of Lithuania as a protectorate under the Swedish Crown with some of the estates being ruled by the Radziwiłł (Radvila) family.

The agreement was short-lived since the Swedish defeat at the Battles of Warka and Prostki and an uprising organised by the pro-Commonwealth nobility in Poland and Lithuania put an end to Swedish power and to the Radziwiłłs' influence.