Short answers, pulled from the story.
The Western Roman Empire ended in 476 when Germanic chieftain Odoacer deposed emperor Romulus Augustulus. This event marked the end of unified political control over Western Europe and triggered centuries of fragmentation.
Emperor Valens died fighting the Goths at the Battle of Adrianople on the 9th of August 378 after their settlement in Thracia failed due to mishandled treatment by Roman officials. The battle culminated from raids that began following the Goths fleeing from the Huns in 376.
Charles the Great, known as Charlemagne, was crowned emperor on Christmas Day 800 creating a Western Roman Empire successor ruling over much of modern France, northern Italy, and Saxony. His systematic expansion beginning in 774 conquered the Lombards and freed the papacy from fear of invasion.
A formal break known as the East-West Schism occurred in 1054 when the papacy and Constantinople patriarchy clashed over authority. Both sides excommunicated each other dividing Christianity into Roman Catholic and Eastern Orthodox branches based on theological differences regarding iconoclasm and clerical marriage.
Between 1347 and 1350 the Black Death killed about one-third of all Europeans while famine plague and warfare devastated populations across the continent. This population decline reversed centuries of growth that had seen Europe expand from 35 million to 80 million people between 1000 and 1347.