Answer:
After Charlemagne united western Europe by defeating the Saxons, he was proclaimed the new "Emporer of Rome" by the Pope in Rome.
Step-by-step explanation:
Charlemagne was the ruler of the Frankish Empire from 768 until his death in 814. He subjugated most of Western Europe in the early Middle Ages and laid the foundation stone for the modern countries of France and Germany. In the year 800 he was crowned Roman Emperor in Rome and was thus the first Germanic prince to assume the Roman imperial title and created the Western European imperial concept that dominated big politics until 1918.
After his father's death in 768, he shared the royal power with his brother Carloman, but when he died in 771, he became the sole ruler. Early on he embarked on a course of great power and crushed in 774 the Lombard Empire and became lord of large parts of Italy. In 777-78, he made a only partially successful campaign against the Arabs in Spain.
Between 773 and 804 he defeated the Saxons, Frisians and Wends, unifying all Western Europe under his domain. On December 25, 800, he was crowned Roman Emperor in Rome by Pope Leo III, becoming equal to the Eastern Roman emperor in Constantinople.