Short answers, pulled from the story.
The Middle Ages began with the fall of the Western Roman Empire, conventionally dated to 476 when Romulus Augustulus was deposed. The end date varies by context: 1453 (fall of Constantinople), 1492 (Columbus's voyage), 1517 (the Reformation), or 1485 (Battle of Bosworth Field) are all used by historians.
A combination of military overextension, economic strain including inflation and rising taxes, external invasions by Germanic tribes, Huns, and others, and internal civil wars weakened the Western Roman Empire over several centuries. The deposition of Romulus Augustulus in 476 by a German chieftain is the traditional marker for the empire's end in the West.
The Black Death killed approximately a third of Europeans between 1347 and 1350. It caused severe population decline, widespread social disruption, peasant revolts, and political instability across the continent, significantly diminishing the population of Europe during the Late Middle Ages.
The Carolingian Empire was a large Frankish realm covering much of Western Europe, including modern-day France, northern Italy, and Saxony. Charlemagne, also known as Charles the Great, built it through systematic expansion beginning in 774. He was crowned emperor on Christmas Day 800, an event regarded as a turning point in medieval history.
The Crusades were military campaigns by Western European Christians aimed at seizing Jerusalem and the Holy Land from Muslim control. The First Crusade was proclaimed by Pope Urban II at the Council of Clermont in 1095, responding to a request from Byzantine Emperor Alexios I Komnenos for aid against Muslim advances. Jerusalem was captured in 1099, and by 1291 all the crusader states had been lost.
Monasteries were among the only centers of literacy and education in early medieval Europe. They copied and preserved manuscripts of classical Latin authors, trained scholars, conducted missions to convert pagan peoples, and served as bases of political and religious influence. Benedict of Nursia wrote the foundational Benedictine Rule for western monasticism in the 6th century, and monks such as Bede, who died in 735, produced significant works of history and theology.