Angrivarii
The wars began in the last years of the reign of Augustus, first emperor of Rome. Augustus died an old but respected man in the year 14 and was celebrated with much pomp and splendor. He left a document to be read to the senate posthumously, expressly forbidding extension of the empire beyond the Rhine. News of the will was welcomed by the Germans, thinking it gave them a free hand in the region. Germanicus found it necessary to pacify the border, which he did by a combination of scorched earth raids and offers of alliance with Rome - in short, stick and carrot. These raids also kept the army of the lower Rhine distracted from the possibility of mutiny, which had broken out on Augustus's death and only been quelled by concessions and executions.
Constitutional reforms of Augustus
Julius Caesar campaigned in Gaul from 59 BC to 49 BC, which granted him unmatched military power and popularity with the people of Rome. With the Gallic Wars concluded, the Senate ordered Caesar to lay down his military command and return to Rome as a "privatus" ("private citizen"). Caesar refused, and marked his defiance in 49 BC by crossing the Rubicon River at the head of his army, leaving his province and illegally entering Roman territory under arms. Civil war resulted, from which Caesar emerged as the unrivaled ruler of Rome.