History of the Balkans in Maps

For a generation after their arrival along the Danube, the Huns were remarkably quiet, but under their new ambitious leader, Attila (who came to power in 433), they began a new wave assault, taking advantage of the weaknesses of both halves of the Empire. By 451, Attila the Hun had defeated all of the Germanic tribes East of the Rhine, but was checked by a German tribe which had resettled west of the Rhine, the Franks. Undeterred, Attila turned south and marched on Rome itself. What happened in this campaign has never been fully explained in terms that we moderns would accept. At the time, however, the explanation was fully acceptable. Marching on the city, Attila was met by the Bishop of Rome, Pope Leo I, who ordered him to stop the attack. At the same time, a huge vision of St. Peter and St. Paul appeared in the sky, and terrified by the apparition, Attila called off the attack, hurridly evacuated the Italian peninsula and died shortly thereafter.
Modern historians offer a more prosaic explanation: over-extended throughout their vast empire, Attila's Huns had failed to develope an administrative system to hold their conquests together. The retreat from Rome encouraged rebellions, and when Attila suddently died the various Germanic tribes took heart. Led by the Gepids, the Germans fell upon the Huns and defeated them at the battle of Nedao, in 454. Attila's numerous sons were more interested in fighting each other for the crown, and within a few years, the bulk of the Huns had retreated from Europe and disappear from history.
By the middle of the fifth century, although the map above shows an intact Western Roman Empire, it lacked leadership and military power. The Bishop of Rome had gained enormous prestige because of the story of his defeat of Atilla, but he had no military authority. In fact, in Italy, the Balkans and the province of Gaul, German tribes, although officially called "allies" had taken over all power.