The study of the famous Belgian historian Henri Pirenne is devoted to the history of Western Europe, the influence that the barbarian invasion of the Roman Empire had on its development, and then the conquest of part of this territory by the Mohammedan Arabs and its inclusion in the Arab Caliphate. The author notes that the German invasion did not violate the Mediterranean unity of the ancient world. The break with the ancient tradition occurred later, and the reason was the rapid spread of Islam as a result of the invasion of the Mohammedan Arabs. As a result, the East was finally separated from the West and Mediterranean unity came to an end. The decline into which the Merovingian monarchy plunged led to the emergence of the Carolingian dynasty. The Pope entered into an alliance with the new dynasty, breaking with the Byzantine emperor, who was no longer able to provide real protection to Rome. The church and feudal lords began to play a dominant role in Europe. Europe showed the world its new face. The Middle Ages began.