Explanation: In the Battle of Teutoburg Forest, a united Germanic force under the command of Arminius, a Germanic prince who had served the Roman Empire and then betrayed it, wiped out three legions (~15,000 men) under the command of Publius Quinctilius Varus. Arminius took this as a prime opportunity to unite Germany under himself as king!
Unfortunately for him, while losing three legions was devastating to Rome's long-term interest in Germany, in the short term, it absolutely enraged them. The future Emperor Tiberius, a dour and miserable son of a bitch, shored up the defences along the border and started making massive raids with total impunity - as the ambush of the three lost legions was due to being (unknowingly) deep in hostile territory - the Germanic tribes had little ability to retaliate into the borders of the Roman Empire itself.
After Tiberius was done raiding and pillaging, the Roman general Germanicus (a name inherited from his father, meaning 'victor over Germania', not a friend of it) went on a several years-long punitive campaign, in which the Roman Legions burned, pillaged, plundered, and generally devastated all of Germania, save for the tribes that had remained allied to them. In the process Arminius's coalition was broken up, and he himself was killed by his countrymen.
Probably wasn't according to Arminius's plans.