The concept of Germany as a distinct region in central Europe can be traced to Roman commander Julius Caesar, who referred to the unconquered area east of the Rhine as "Germania", thus distinguishing it from Gaul (France), which he had conquered. The victory of the Germanic tribes in the Battle of the Teutoburg Forest (AD 9) prevented annexation by the Roman Empire, although the Roman provinces of Germania Superior and Germania Inferior were established along the Rhine. Following the Fall of the Western Roman Empire, the Franks conquered the other West Germanic tribes. When the Frankish Empire was divided among Charlemagne's heirs in 843, the eastern part became East Francia. In 962, Otto I became the first emperor of the Holy Roman Empire, the medieval German state. 

In the High Middle Ages, the regional dukes, princes and bishops gained power at the expense of the emperors. Martin Luther led the Protestant Reformation against the Catholic Church after 1517, as the northern states became Protestant, while the southern states remained Catholic. The two parts of the Holy Roman Empire clashed in the Thirty Years' War (1618–1648), which was ruinous to the twenty million civilians living in both parts. The Thirty Years' War brought tremendous destruction to Germany; more than 1/4 of the population and 1/2 of the male population in the German states were killed by the catastrophic war. 1648 marked the effective end of the Holy Roman Empire and the beginning of the modern nation-state system, with Germany divided into numerous independent states, such as Prussia, Bavaria and Saxony.
how far back can the concept of Germany be traced?
traced to Roman commander Julius Caesar