Question: Who was in charge of the country beaten at the Battle of Kosovo?

full_context: Document 1: Ottoman Empire: The son of Murad II, Mehmed the Conqueror, reorganized the state and the military, and conquered Constantinople on 29 May 1453. Mehmed allowed the Orthodox Church to maintain its autonomy and land in exchange for accepting Ottoman authority. Because of bad relations between the states of western Europe and the later Byzantine Empire, the majority of the Orthodox population accepted Ottoman rule as preferable to Venetian rule. Albanian resistance was a major obstacle to Ottoman expansion on the Italian peninsula.
Document 2: President of Russia: The president is elected directly through a popular vote to a six - year term. The law prohibits anyone from ever being elected to the presidency for a third consecutive term. In all, three individuals have served four presidencies spanning six full terms. On 7 May 2012, Vladimir Putin became the fourth and current president.
Document 3: Portugal: The Head of State of Portugal is the President of the Republic, elected to a five-year term by direct, universal suffrage. He or she has also supervision and reserve powers. These powers are often compared[by whom?] with the "moderator power" that was held by the King in the Portuguese Constitutional Monarchy.[citation needed] Presidential powers include the appointment of the Prime Minister and the other members of the Government (where the President takes into account the results of legislative elections); dismissing the Prime Minister; dissolving the Assembly of the Republic (to call early elections); vetoing legislation (which may be overridden by the Assembly with a supermajority); and declaring a state of war or siege. The President is also the ex officio Commander-in-Chief of the Armed Forces.
Document 4: Southern Europe: The Late Middle Ages represented a period of upheaval in Europe. The epidemic known as the Black Death and an associated famine caused demographic catastrophe in Europe as the population plummeted. Dynastic struggles and wars of conquest kept many of the states of Europe at war for much of the period. In the Balkans, the Ottoman Empire, a Turkish state originating in Anatolia, encroached steadily on former Byzantine lands, culminating in the Fall of Constantinople in 1453.
Document 5: Ottoman Empire: In the century after the death of Osman I, Ottoman rule began to extend over the Eastern Mediterranean and the Balkans. Osman's son, Orhan, captured the northwestern Anatolian city of Bursa in 1324, and made it the new capital of the Ottoman state. This Ottoman conquest meant the loss of Byzantine control over northwestern Anatolia. The important city of Thessaloniki was captured from the Venetians in 1387. The Ottoman victory at Kosovo in 1389 effectively marked the end of Serbian power in the region, paving the way for Ottoman expansion into Europe. The Battle of Nicopolis in 1396, widely regarded as the last large-scale crusade of the Middle Ages, failed to stop the advance of the victorious Ottoman Turks.
Document 6: Middle Ages: Although the Palaeologi emperors recaptured Constantinople from the Western Europeans in 1261, they were never able to regain control of much of the former imperial lands. They usually controlled only a small section of the Balkan Peninsula near Constantinople, the city itself, and some coastal lands on the Black Sea and around the Aegean Sea. The former Byzantine lands in the Balkans were divided between the new Kingdom of Serbia, the Second Bulgarian Empire and the city-state of Venice. The power of the Byzantine emperors was threatened by a new Turkish tribe, the Ottomans, who established themselves in Anatolia in the 13th century and steadily expanded throughout the 14th century. The Ottomans expanded into Europe, reducing Bulgaria to a vassal state by 1366 and taking over Serbia after its defeat at the Battle of Kosovo in 1389. Western Europeans rallied to the plight of the Christians in the Balkans and declared a new crusade in 1396; a great army was sent to the Balkans, where it was defeated at the Battle of Nicopolis. Constantinople was finally captured by the Ottomans in 1453.
Document 7: Portugal: The President, who is elected to a five-year term, has an executive role: the current President is Aníbal Cavaco Silva. The Assembly of the Republic is a single chamber parliament composed of 230 deputies elected for a four-year term. The Government is headed by the Prime Minister (currently António Costa) and includes Ministers and Secretaries of State. The Courts are organized into several levels, among the judicial, administrative and fiscal branches. The Supreme Courts are institutions of last resort/appeal. A thirteen-member Constitutional Court oversees the constitutionality of the laws.
Document 8: Mali: The president serves as a chief of state and commander in chief of the armed forces. A prime minister appointed by the president serves as head of government and in turn appoints the Council of Ministers. The unicameral National Assembly is Mali's sole legislative body, consisting of deputies elected to five-year terms. Following the 2007 elections, the Alliance for Democracy and Progress held 113 of 160 seats in the assembly. The assembly holds two regular sessions each year, during which it debates and votes on legislation that has been submitted by a member or by the government.
Document 9: Ottoman Empire: Part of the Ottoman territories in the Balkans (such as Thessaloniki, Macedonia and Kosovo) were temporarily lost after 1402 but were later recovered by Murad II between the 1430s and 1450s. On 10 November 1444, Murad II defeated the Hungarian, Polish, and Wallachian armies under Władysław III of Poland (also King of Hungary) and John Hunyadi at the Battle of Varna, the final battle of the Crusade of Varna, although Albanians under Skanderbeg continued to resist. Four years later, John Hunyadi prepared another army (of Hungarian and Wallachian forces) to attack the Turks but was again defeated by Murad II at the Second Battle of Kosovo in 1448.
Document 10: President of South Africa: The President is elected by the National Assembly, the lower house of Parliament, and is usually the leader of the largest party, which has been the African National Congress since the first non-racial elections were held on 27 April 1994. The Constitution limits the president's time in office to two five - year terms. The first president to be elected under the new constitution was Nelson Mandela. The incumbent is Cyril Ramaphosa, who was elected by the National Assembly on 15 February 2018 following the resignation of Jacob Zuma.
Document 11: Middle Ages: In the 11th century, the Seljuk Turks took over much of the Middle East, occupying Persia during the 1040s, Armenia in the 1060s, and Jerusalem in 1070. In 1071, the Turkish army defeated the Byzantine army at the Battle of Manzikert and captured the Byzantine Emperor Romanus IV (r. 1068–71). The Turks were then free to invade Asia Minor, which dealt a dangerous blow to the Byzantine Empire by seizing a large part of its population and its economic heartland. Although the Byzantines regrouped and recovered somewhat, they never fully regained Asia Minor and were often on the defensive. The Turks also had difficulties, losing control of Jerusalem to the Fatimids of Egypt and suffering from a series of internal civil wars. The Byzantines also faced a revived Bulgaria, which in the late 12th and 13th centuries spread throughout the Balkans.
Document 12: Ottoman Greece: With no further threat by the Serbs and the subsequent Byzantine civil wars, the Ottomans besieged and took Constantinople in 1453 and then advanced southwards into Greece, capturing Athens in 1458. The Greeks held out in the Peloponnese until 1460, and the Venetians and Genoese clung to some of the islands, but by the early 16th century all of mainland Greece and most of the Aegean islands were in Ottoman hands, excluding several port cities still held by the Venetians (Nafplio, Monemvasia, Parga and Methone the most important of them). The mountains of Greece were largely untouched, and were a refuge for Greeks who desired to flee Ottoman rule and engage in guerrilla warfare.
Document 13: Greece: In the 14th century, much of the Greek peninsula was lost by the Byzantine Empire at first to the Serbs and then to the Ottomans. By the beginning of the 15th century, the Ottoman advance meant that Byzantine territory in Greece was limited mainly to its then-largest city, Thessaloniki, and the Peloponnese (Despotate of the Morea). After the fall of Constantinople to the Ottomans in 1453, the Morea was the last remnant of the Byzantine Empire to hold out against the Ottomans. However, this, too, fell to the Ottomans in 1460, completing the Ottoman conquest of mainland Greece. With the Turkish conquest, many Byzantine Greek scholars, who up until then were largely responsible for preserving Classical Greek knowledge, fled to the West, taking with them a large body of literature and thereby significantly contributing to the Renaissance.
Document 14: Tomislav Nikolić: Tomislav Nikolić (, ; born 15 February 1952) is a Serbian politician who served as the President of Serbia from 2012 to 2017. He is also the founder of the Serbian Progressive Party, and he led the party until his election as President. In the 2012 presidential election, he was elected to a five-year term as President in a second round of voting.
Document 15: Serbia: The President of the Republic ("Predsednik Republike") is the head of state, is elected by popular vote to a five-year term and is limited by the Constitution to a maximum of two terms. In addition to being the commander in chief of the armed forces, the president has the procedural duty of appointing the prime minister with the consent of the parliament, and has some influence on foreign policy. Aleksandar Vučić of the Serbian Progressive Party is the current president following the 2017 presidential election. Seat of the presidency is Novi Dvor.
ground_truth: Aleksandar Vučić
sub_queries: Who was defeated at the Battle of Kosovo? Answer: Serbia
Who was in charge of Serbia ? Answer: Aleksandar Vučić