Explanation: One of Caesar's major justifications for warring in Gaul with a massive military force was... that he was literally asked to.

You see, some of the Gallic tribes had requested help from a neighboring Germanic warlord, Ariovistus, in the neverending tribal disputes of Gaul. But said Germanic warlord decided he rather liked Gaul, and instead settled in as an overlord, extracting tribute from the Gauls who had asked him for protection.

The Gauls then asked Caesar, who had pursued a migrating tribe into Gaul in order to 'protect' Gallic interests, to expel Ariovistus for them. Caesar did so. And then Caesar decided he rather liked Gaul, and instead settled Rome in as overlord, extracting tribute from the Gauls who had asked him for protection...