Duchy of Livonia in the context of "Union of Lublin"

The Union of Grodno established a real union between the Grand Duchy of Lithuania and the Duchy of Livonia on 25 December 1566, during the Livonian War. Livonia had submitted itself to Sigismund II Augustus by the Treaty of Vilnius (1561). 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.

Subdivisions of the Polish–Lithuanian Commonwealth evolved over for centuries of its existence from the signing of the Union of Lublin to the third partition.

The lands that once belonged to the Commonwealth are now largely distributed among several central, eastern, and northern European countries: Poland (except western Poland), Lithuania, Latvia, Belarus, most of Ukraine, parts of Russia, southern half of Estonia, and smaller pieces in Slovakia and Moldova.

The Lithuanian nobility (Lithuanian: bajorija) or szlachta of the Grand Duchy of Lithuania (Lithuanian: Lietuvos Didžiosios Kunigaikštystės šlėkta, Polish: szlachta Wielkiego Księstwa Litewskiego) was historically a legally privileged hereditary elite class in the Grand Duchy of Lithuania and Polish Lithuanian Commonwealth (including during period of foreign rule 1795–1918) consisting of Lithuanians from Lithuania Proper; Samogitians from Duchy of Samogitia; following Lithuania's eastward expansion into what is now Belarus, Ukraine and Russia, many ethnically Ruthenian noble families (boyars); and, later on, predominantly Baltic German families from the Duchy of Livonia and Inflanty Voivodeship.

Initially, the privileged social group of the Grand Duchy of Lithuania was called boyars. Boyars became part of the szlachta (nobility) during the Union of Horodło on October 2, 1413, initiating nobility in the Grand Duchy of Lithuania following the Western European model (with a hereditary system of heraldic identification), as well as an increase in the position of the Greater Lithuanian nobility. The Grand Duchy of Lithuania adopted Polish institutions of castellans and voivodes, and 47 selected boyars of Grand Duchy of Lithuania of the Catholic faith were adopted by Polish noble families and received Polish coats of arms.

Wenden Voivodeship (Polish: Województwo wendeńskie, Lithuanian: Vendeno vaivadija) was a unit of administrative division and local government in the Duchy of Livonia, part of the Polish–Lithuanian Commonwealth. It was formed in 1598 by King Sigismund III Vasa, out of Wenden Presidency (Province), which had been created in 1582 by King Stephen Báthory, after the Truce of Yam-Zapolsky. The voivodeship remained in the Commonwealth until the Swedish Empire's conquest of Livonia in the 1620s. The unconquered remainder of Livonia was named Inflanty Voivodeship, and continued to be part of the Commonwealth until its first partition in 1772.

Officially, Wenden Voivodeship belonged to Poland–Lithuania until the Treaty of Oliva in 1660. Its capital was Wenden, where local sejmiks of the nobility (see szlachta) took place. Wenden Voivodeship elected two deputies to the Sejm of the Polish–Lithuanian Commonwealth. Even though it no longer belonged to the Commonwealth after the Swedish conquest, its voivodes continued to be named by Polish kings until the final partition of Poland (1795), as the so-called "fictitious titles" (Polish: urzędy fikcyjne).

The Treaty of Vilnius was concluded on 28 November 1561, during the Livonian War, between the Livonian Confederation and the Grand Duchy of Lithuania in Vilnius. With the treaty, the non-Danish and non-Swedish part of Livonia, with the exception of the Free imperial city of Riga, subjected itself to the Grand Duke of Lithuania, Sigismund II Augustus with the Pacta subiectionis (Provisio ducalis). In turn, Sigismund granted protection from the Tsardom of Russia and confirmed the Livonian estates' traditional privileges, laid out in the Privilegium Sigismundi Augusti.

The secularization of the Livonian Order was the "final act" in Livonia's transition from the Middle Ages to the Early Modern era. The territories were re-organized in the Duchy of Courland and Semigallia and the Duchy of Livonia, the latter competing with the Kingdom of Livonia during the war. After its reconquest, Sigismund's successor Stephen Báthory ignored the privileges of 1561, granted a new constitution and initiated Counter-Reformation. These measures were reversed after the Swedish conquest. When after a further series of wars Livonia capitulated to Russia in 1710, the Privilegium Sigismundi Augusti was confirmed by Peter the Great.