Read this: The Bulgarian Empire was in decline by the 14th century, and the ascendancy of Serbia was marked by the Serbian victory over the Bulgarians in the Battle of Velbazhd in 1330. By 1346, the Serbian king Stefan Dusan had been proclaimed emperor. Yet Serbian dominance was short-lived; the Serbian army led by the Lazar Hrebljevanovic was defeated by the Ottomans at the Battle of Kosovo in 1389, where most of the Serbian nobility was killed and the south of the country came under Ottoman occupation, as much of southern Bulgaria had become Ottoman territory in 1371. Northern remnants of Bulgaria were finally conquered by 1396, Serbia fell in 1459, Bosnia in 1463, and Albania was finally subordinated in 1479 only a few years after the death of Skanderbeg. Belgrade, an Hungarian domain at the time, was the last large Balkan city to fall under Ottoman rule, in 1521. By the end of the medieval period, the entire Balkan peninsula was annexed by, or became vassal to, the Ottomans.

In what year was the Battle of Kosovo?
What is the answer? (If it cannot be answered, return "unanswerable")
1389