Why go
The Rhine and Danube were frontier zones, not old national borders. Knowing that makes Roman remains in the west and south, and later Frankish history, easier to place. The defeat of Roman forces under Varus and the rise of Charlemagne belong to different chapters of this long transition.
The full story
Groups later described as Germanic moved and settled across northern and central Europe over centuries. Their histories were not identical. Rome advanced toward the Rhine and Danube under Augustus, but in 9 CE forces led by Arminius defeated three Roman legions under Varus. Parts of today's western and southern Germany nevertheless remained within Roman provinces. The frontier was a zone of contact and exchange as well as conflict. From the third century, larger groupings such as the Franks, Alemanni, Saxons, and Thuringians became prominent. The weakening of western Roman power and later migrations changed the political map. The Franks came to control extensive western and central lands, while Saxon and Slavic communities occupied parts of the north and east. Under the Carolingians, especially Charlemagne, the Frankish realm reached across much of western and central Europe. Its division in the ninth century helped form an eastern kingdom that later became central to German history. None of these early peoples should be read as a direct equivalent of the modern nation.