What is the theme in The Conquest of Gaul by Julius Caesar?

The Germans are a main theme. Throughout his accounts of the campaigns in Gaul in the years 58-51 BC, there is a constant expression of the threats presented by the German tribes east of the Rhine. In the first campaign, Caesar conquers the encroaching Germans and their king Ariovistus. To do so, he has to deal with the widespread fear of the Germans in the minds of the Gauls and of his own troops. The Germans are regarded as being of enormous stature, having incredible courage, and possessing splendid military training. They have overcome parts of Gaul and have caused the Helvetii and other tribes to move westwards. In his speech to the centurions at Besançon, Caesar acknowledges the domination of the Germans over the Gauls and refers to the rebellion of Spartacus, where several Roman armies were overcome with the help of German troops. In driving Ariovistus back across the Rhine, Caesar scores an important victory.