 Complete the following phrase:  In the third century BC, a Eurasian nomadic people, the Xiongnu, began threatening Chinas frontiers, but by the first century BC, they had been completely expelled. They then turned their attention westward and displaced various other tribes in Eastern and Central Europe, which led to a cascade of events. Attila rose to power as leader of the Huns and initiated a campaign of invasions and looting and went as far as Gaul modern-day France. Attilas Huns were clashing with the Roman Empire, which had already been divided into two halves for ease of administration: the Eastern Roman Empire and the Western Roman Empire. Despite their decisive victory at the Battle of Chalons in 451 AD, the Romans were unable to stop Attila from attacking Roman Italy. Northern Italian cities like Milan were ravaged. The Huns never again posed a threat to the Romans after Attilas death, but the rise of the Huns also forced the Germanic peoples out of their territories and made those groups press their way into parts of France, Spain, Italy, and even as far south as North Africa. The city of Rome itself came under attack by the Visigoths in 