Diet (Soim; Polish: Sejm). Legislative assembly of a national or provincial stature. The following states, which included some part of Ukrainian territory, had a diet: the Grand Duchy of Lithuania, the Polish Commonwealth, Austria-Hungary, the Republic of Poland (1921–39), Slovakia, and Carpatho-Ukraine (1939).
In the Grand Duchy of Lithuania the Great Diet (Soim Velykyi Valnyi) as a central representative and estate institution was well established by the end of the 15th century, although it did not attain its final form as the body representing the nobility's interests until the Second Lithuanian Statute of 1566. Its powers were limited by the powers of the Council of Lords and of the grand duke, and its main role was to approve legislation and state taxes.
After the Union of Lublin in 1569, the Great Diet of Lithuania and the Diet of Poland, which had existed since the 14th century, merged into one diet, the Sejm, for the whole Polish-Lithuanian Commonwealth. This diet became the highest legislative body. It consisted of the king, the senate, and the chamber of deputies, which had the decisive voice. The deputies to the chamber were elected at local dietines (see Dietine) of the nobility. The Sejm's adoption of the principle of unanimity, which eventually gave a single deputy the right to overrule the decision of the entire diet (liberum veto), led to a paralysis of the Polish diet and state in the 18th century. The ordinary diet convened biannually for six weeks in alternating cities—twice in Warsaw and then once in Hrodna. There also existed extraordinary diets: convocational diets (during an interregnum), elective diets (for electing a new king), coronational diets (in Cracow), and emergency diets (called by the king).
With the introduction of autonomy in the crown lands of Austria, provincial diets were established in Galicia and Bukovyna in 1861, and they functioned until 1918. Jurisdiction over educational, economic, and other affairs was transferred to them from the parliament in Vienna. Because of the curial electoral system, the Ukrainian deputies had little influence in the provincial diets .
According to the constitution of 1921, the Polish chamber of deputies in the parliament was to be known as the Sejm (Diet). Its wide range of powers was reduced while the Senate's powers were increased after Józef Piłsudski's coup d'état in May 1926 and again by the constitution of 1935. (See also Parliament, Diet of Carpatho-Ukraine.)