He helped Europeans realize they share the same traits with different religions, such as the religions you listed. Charlemagne was also interested in renewing the idea of the Holy Roman Empire, which basically made Christians and Germans come together.
Charlemagne blended Roman, German, and Christian traditions through cultural revival by crowning himself Emperor, integrating Christianity into governance, commissioning Roman-style architecture, promoting learning, and establishing diplomatic relations. His reign laid the foundation for the Holy Roman Empire, creating a cohesive society that combined these diverse influences.
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