Page "Alemanni" Paragraph 11

Caracalla left for the frontier, where for the rest of his short reign he was known for his unpredictable and arbitrary operations launched by surprise after a pretext of peace negotiations.

If he had any reasons of state for such actions they remained unknown to his contemporaries.

Whether or not the Alemanni had been previously neutral, they were certainly further influenced by Caracalla to become thereafter notoriously implacable enemies of Rome.