Excerpts from Books and Wikipedia
"Meanwhile, another part of the western empire disappeared. In 429, the king of the Vandals in Hispania, Geiseric, built a fleet of ships and sailed across the mouth of the Mediterranean Sea. He then began to march along the North African coast, conquering his way through Roman provinces and independent African kingdoms alike. By 430, he had reached the Roman city of Hippo Regius. His army laid siege to it while the elderly bishop Augustine lay inside, suffering from his final illness. The siege dragged on for eighteen months; the man who had written of the ultimate triumph of the kingdom of God died with Vandals still surrounding his city and no hope of relief. When Hippo fell, Geiseric marched on to Carthage. It was defeated and overrun in 431; Geiseric lined up the Roman soldiers who had defended it, forced them to swear an oath that they would never again fight against a Vandal army, and then let them go. North Africa was lost to Rome. Before long Geiseric decided to concentrate his energies on his North African holdings. He abandoned Hispania and ruled as a North African pirate-king, his headquarters at Carthage, master of a powerful Vandal kingdom that . . ."