The Union of Grodno established a

real union Real union is a union of two or more states, which share some state institutions in contrast to personal unions; however, they are not as unified as states in a political union. It is a development from personal union and has historically be ...

between the

Grand Duchy of Lithuania The Grand Duchy of Lithuania was a European state that existed from the 13th century to 1795, when the territory was Partitions of Poland, partitioned among the Russian Empire, the Kingdom of Prussia, and the Habsburg Empire, Habsburg Empire of ...

and the

Duchy of Livonia The Duchy of Livonia ( or ; lt, Livonijos kunigaikštystė; la, Ducatus Ultradunensis; et, Liivimaa hertsogkond; lv, Pārdaugavas hercogiste; german: Herzogtum Livland), also referred to as Polish Livonia or Livonia ( pl, link=no, Inflanty) ...

on 25 December 1566, during the

Livonian War The Livonian War (1558–1583) was the Russian invasion of Old Livonia, and the prolonged series of military conflicts that followed, in which Tsar Ivan the Terrible of Russia (Muscovy) unsuccessfully fought for control of the region (pr ...

. Livonia had submitted itself to

Sigismund II Augustus Sigismund II Augustus ( pl, Zygmunt II August, lt, Žygimantas Augustas; 1 August 1520 – 7 July 1572) was King of Poland and Grand Duke of Lithuania, the son of Sigismund I the Old, whom Sigismund II succeeded in 1548. He was the first ruler ...

by the

Treaty of Vilnius (1561) A treaty is a formal, legally binding written agreement between actors in international law. It is usually made by and between sovereign states, but can include international organizations, individuals, business entities, and other legal perso ...

. Livonia's administrative division was re-organized with its castellans becoming members of the Lithuanian senate. The union did not impact Livonian jurisdiction, which was to be carried out according to its traditional customs.

Sources

* * Livonian War 1566 treaties Treaties of the Grand Duchy of Lithuania Treaties of the Duchy of Livonia 1566 in Lithuania {{Lithuania-hist-stub