Question: Before 21 Lithuanian dukes signed a peace treaty with Galicia–Volhynia, what is an example of the war-related functions the group who made up the majority of the military-economic staff of the state performed?

Context paragraphs:
U.S.–German Peace Treaty (1921): The U.S.—German Peace Treaty is a peace treaty between the U.S. and German governments, signed in Berlin on August 25, 1921, in the aftermath of World War I.  The main reason for the conclusion of that treaty was the fact that the U.S. Senate did not consent to ratification of the multilateral peace treaty signed in Versailles, thus leading to a separate peace treaty.  Ratifications were exchanged in Berlin on November 11, 1921, and the treaty became effective on the same day.  The treaty was registered in "League of Nations Treaty Series" on August 12, 1922.

Leičiai: Leičiai (singular: leitis) were a distinct social group of the Lithuanian society in the early Grand Duchy of Lithuania subordinate to the Lithuanian ruler or the state itself.  Leičiai were native to the Lietuva Land and formed the core of the Lithuanian society in the pre-state era and during the establishment of the state.  Leičiai made up the majority of the military-economic staff of the state: they enforced state authority in the periphery, protected state borders, and performed various other war-related functions, such as breeding riding horses.  By the 15th and 16th centuries, leičiai were in decline, already losing some of their functions and prestige, and they disappeared as a social class after the implementation of the Wallach Reform.

Poles in Ukraine: The Polish minority in Ukraine officially numbers about 144,130 (according to the 2001 census), of whom 21,094 (14.6%) speak Polish as their first language.  The history of Polish settlement in current territory of Ukraine dates back to 1030–31.  In Late Middle Ages, following the extinction of Rurikid dynasty in 1323, the Kingdom of Poland extended east in 1340 to include the lands of Przemyśl and in 1366, Kamianets-Podilskyi (Kamieniec Podolski).  The settlement of Poles became common there after the Polish–Lithuanian peace treaty signed in 1366 between Casimir III the Great of Poland, and Liubartas of Lithuania.  Following the Union of Lublin (1569), principalities of Galicia and Western Volhynia were incorporated into the Crown of the Kingdom of Poland as the Ruthenian Voivodeship, while the rest of Red Ruthenia together with Kiev came under Lithuanian control.

Treaty of Taipei: The Sino-Japanese Peace Treaty (Chinese: 中日和平條約 ), commonly known as the Treaty of Taipei (), was a peace treaty between Japan and the Republic of China (ROC) signed in Taipei, Taiwan on April 28, 1952, and took effect on August 5 the same year, marking the formal end of the Second Sino-Japanese War (1937–45).  This treaty was necessary, because neither the Republic of China nor the People's Republic of China was invited to sign the Treaty of San Francisco due to disagreements by other countries as to which government was the legitimate government of China during and after the Chinese Civil War.  Under pressure from the United States, Japan signed a separate peace treaty with the Republic of China to bring the war between the two states to a formal end with a victory for the ROC.  Although the ROC itself was not a participant in the San Francisco Peace Conference due to the resumption of the Chinese Civil War after 1945, this treaty largely corresponds to that of San Francisco.  In particular, the ROC waived service compensation to Japan in this treaty with respect to Article 14(a).1 of the San Francisco Treaty.

Dausprungas: Dausprungas (also "Dovsprunk" in Russian sources, died before 1238) was the older brother of Mindaugas, the first King of Lithuania.  Dausprungas is mentioned in the peace treaty with Galicia–Volhynia in 1219 among the 21 early dukes of Lithuania as one of the five elder dukes, the other four being Živinbudas, Daujotas, Mindaugas and Viligaila (Daujotas' brother).  Since Dausprungas is the only known brother of Mindaugas, Mindaugas' nephews Edivydas and Tautvilas are presumed to be his sons.  If that is true, then Dausprungas is father-in-law of Daniel of Halych and he was also married to Vykintas' sister.  Because it is known that Mindaugas used to kill his relatives to gain power and because Dausprungas is not mentioned in any other sources, some imply that he was killed by Mindaugas, but others rebut since his sons still ruled their lands in 1248.

Galicia–Volhynia Wars: Galicia–Volhynia Wars were several wars fought in the years 1340–1392 over the succession in the Principality of Galicia–Volhynia (in modern Poland and Ukraine).  After Boleslaw-Yuri II was poisoned by local nobles in 1340, both Grand Duchy of Lithuania and Kingdom of Poland advanced claims over the principality.  After a prolonged conflict, Galicia–Volhynia was divided between Poland (Galicia) and Lithuania (Volhynia) and the principality ceased to exist as an independent state.  Poland acquired a territory of approximately 52000 km2 with 200,000 inhabitants.

Vilikaila: Vilikaila or Viligaila was one of the 5 elder Lithuanian dukes mentioned in the peace treaty with Halych-Volhynia in 1219.  He is mentioned as brother of Daujotas, which leads scholars to believe he was the younger or perhaps less influential brother.  The brothers are not mentioned in any other sources.  Tomas Baranauskas, a modern Lithuanian historian, believes that Vilikaila and Daujotas might be sons of Stekšys, a Lithuanian duke killed in 1214.

History of Lithuania (1219–95): The history of Lithuania between 1219 and 1295 concerns the establishment and early history of the first Lithuanian state, the Grand Duchy of Lithuania.  The beginning of the 13th century marks the end of the prehistory of Lithuania.  From this point on the history of Lithuania is recorded in chronicles, treaties, and other written documents.  In 1219, 21 Lithuanian dukes signed a peace treaty with Galicia–Volhynia.  This event is widely accepted as the first proof that the Baltic tribes were uniting and consolidating.  Despite continuous warfare with two Christian orders, the Livonian Order and the Teutonic Knights, the Grand Duchy of Lithuania was established and gained some control over the lands of Black Ruthenia, Polatsk, Minsk, and other territories east of modern-day Lithuania that had become weak and vulnerable after the collapse of Kievan Rus'.

Kingdom of Galicia–Volhynia: The Principality of Galicia–Volhynia, or Kingdom of Rus' (Old Ruthenian: Галицко-Волинскоє князство, Королѣвство Русь , Ukrainian: Галицько-Волинське князівство, Королівство Русі , Polish: "Królestwo Galicji-Wołyn" , Slovak: "Kráľovstvo Galícii-Volyni" , Latin: "Regnum Galiciae et Lodomeriae, Regnum Russiae" ), was a state in the regions of Galicia and Volhynia, of present-day western Ukraine, that was formed after the conquest of Galicia by the Prince of Volhynia Roman the Great with the help of Leszek the White of Poland.  Roman the Great united the principalities of Halych (Galicia) and Volhynia into a state that existed from 1199 to 1349.  Along with Novgorod and Vladimir-Suzdal, it was one of the three most important powers to emerge from the collapse of Kievan Rus'.

Daujotas: Daujotas was one of the 5 elder Lithuanian dukes mentioned in the peace treaty with Halych-Volhynia in 1219.  In the same document Vilikaila is mentioned as brother of Daujotas which suggests that Daujotas was the older or perhaps more influential brother.  The brothers are not mentioned in any other sources.  Tomas Baranauskas, a modern Lithuanian historian, believes that Vilikaila and Daujotas might be sons of Stekšys, a Lithuanian duke killed in 1214.

Supporting paragraphs: Leičiai History of Lithuania (1219–95)
Answer: breeding riding horses