There are several reasons why Germanic tribes began invading the Roman Empire, but in general the main reason was that they knew the empire was overstretched.
While the Goths were invading and settling in Rome, another Germanic tribe was also attempting to take control of the Empire. The Vandals were a Germanic tribe that had a habit of looting the cities they invaded. ... The Vandals held power over Rome until they were defeated by the Romans in 533.
